Dejerine-Sottas综合征致病机制的研究进展

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BackgroundThe Charcot-Marie-Tooth (CMT) phenotype caused by mutation in the myelin protein zero (MPZ) gene varies considerably, from early onset and severe forms to late onset and milder forms. The mechanism is not well understood. The myelin protein zero (P0) mediates adhesion in the spiral wraps of the Schwann cell's myelin sheath. The crystalline structure of the extracellular domain of the myelin protein zero (P0ex) is known, while the transmembrane and intracellular structure is unknown.FindingsOne novel missense mutation caused a milder late onset CMT type 2, while the second missense mutation caused a severe early onset phenotype compatible with Déjérine-Sottas syndrome.ConclusionsThe phenotypic variation caused by different missense mutations in the MPZ gene is likely caused by different conformational changes of the MPZ protein which affects the functional tetramers. Severe changes of the MPZ protein cause dysfunctional tetramers and predominantly uncompacted myelin, i.e. the severe phenotypes congenital hypomyelinating neuropathy and Déjérine-Sottas syndrome, while milder changes cause the phenotypes CMT type 1 and 2.

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Hereditary demyelinating peripheral neuropathies consist of a heterogeneous group of genetic disorders that includes hereditary neuropathy with liability to pressure palsies (HNPP), Charcot-Marie-Tooth disease (CMT), Dejerine-Sottas syndrome (DSS), and congenital hypomyelination (CH). The clinical classification of these neuropathies into discrete categories can sometimes be difficult because there can be both clinical and pathologic variation and overlap between these disorders. We have identified five novel mutations in the myelin protein zero (MPZ) gene, encoding the major structural protein (P0) of peripheral nerve myelin, in patients with either CMT1B, DSS, or CH. This finding suggests that these disorders may not be distinct pathophysiologic entities, but rather represent a spectrum of related "myelinopathies" due to an underlying defect in myelination. Furthermore, we hypothesize the differences in clinical severity seen with mutations in MPZ are related to the type of mutation and its subsequent effect on protein function (i.e., loss of function versus dominant negative).

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Dejerine‐Sottas syndrome (DSS), a severe demyelinating peripheral neuropathy with onset in infancy, has been associated with mutations in either PMP22 or MPZ. Most cases of DSS are caused by a single heterozygous dominant point mutation. We identified three de novo point mutations in MPZ exon 3 in a sporadic DSS patient. These three point mutations occur on the same allele and result in three novel amino acid substitutions: Ile(85)Thr, Asn(87)His, and Asp(99)Asn. Our data raise the question as to the potential mechanism(s) involved in the formation of multiple point mutations at a given locus. Hum Mutat 10:21–24, 1997. © 1997 Wiley‐Liss, Inc.

Objective – To describe a patient with the Dejerine–Sottas’ syndrome due to a de novo Ser72Leu amino acid substitution in the PMP22 protein and summarize the phenotype associated with this frequent mutation.

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Background. PMP22-related neuropathies comprise a spectrum of predominantly demyelinating disorders, most commonly Charcot–Marie–Tooth type 1A (CMT1A; 17p12 duplication) and hereditary neuropathy with liability to pressure palsies (HNPP; 17p12 deletion), with rarer phenotypes due to PMP22 sequence variants (CMT1E, Dejerine–Sottas syndrome [DSS]). Methods. We conducted a PRISMA-compliant systematic review (PROSPERO ID: 1139921) of PubMed and Scopus (January 2015–August 2025). Eligible studies reported genetically confirmed PMP22-related neuropathies with clinical and/or neurophysiological data. Owing to heterogeneous reporting, we synthesized pooled counts and proportions without meta-analysis, explicitly tracking missing denominators. Results. One hundred twenty-seven studies (n = 4493 patients) were included. Sex was available for 995 patients (males 53.8% [535/995]; females 46.2% [460/995]); mean age at onset was 23.7 years in males and 16.4 years in females. Phenotypic classification was reported for 4431/4493 (75.4% CMT1A, 20.9% HNPP, 2.6% CMT1E, 1.2% DSS). Across phenotypes, weakness/foot drop was the leading presenting symptom when considering only cohorts that explicitly reported it (e.g., 65.3% in CMT1A; 76.0% in HNPP); sensory complaints (numbness, paresthesia/dysesthesia) were variably documented. Neurophysiology consistently showed demyelinating patterns, with median and ulnar nerves most frequently abnormal among assessed nerves; in HNPP, deep peroneal and sural involvement were also common in evaluated subsets. Comorbidities clustered by phenotype: orthopedic/neuromuscular features (pes cavus/hammer toes, scoliosis/kyphosis, tremor) in CMT1A and DSS; broader metabolic/autoimmune and neurodevelopmental associations in HNPP; and higher syndromic/ocular/hearing involvement in CMT1E. Genetically, 75.6% (3241/4291) had 17p12 duplication, 19.6% (835/4291) 17p12 deletion, and 4.8% (215/4291) PMP22 sequence variants with marked allelic heterogeneity. Among 2571 cases with available methods, MLPA was most used (41.9%), followed by NGS (20.4%) and Sanger sequencing (17.8%). Main limitations include heterogeneous and incomplete reporting across studies (especially symptoms and nerve-specific data) and the absence of a formal risk-of-bias appraisal, which preclude meta-analysis and may skew phenotype proportions toward more frequently reported entities (e.g., CMT1A). Conclusions. Recent literature confirms that PMP22 copy-number variants account for the vast majority of cases, while sequence-level variants underpin a minority with distinct phenotypes (notably CMT1E/DSS). Routine MLPA, complemented by targeted/NGS, optimizes diagnostic yield. Standardized reporting of nerve-conduction parameters and symptom denominators is urgently needed to enable robust cross-study comparisons in both pediatric and adult populations.

Hereditary polyneuropathies represent a genetically and clinically heterogeneous group of disorders affecting the peripheral nervous system, characterized by progressive motor, sensory, and autonomic impairment. Advances in molecular genetics have identified key causative genes, including PMP22, MPZ, MFN2, TTR, EGR2, and CX32 (GJB1), which are implicated in Charcot–Marie–Tooth disease, Dejerine–Sottas syndrome, and related neuropathies. These conditions display substantial allelic and locus heterogeneity. Pathogenetically, mechanisms involve impaired myelin maintenance, disrupted axonal transport, mitochondrial dysfunction, and aberrant Schwann cell biology. Despite these insights, therapeutic options remain limited, and there is a pressing need to translate genetic findings into effective interventions. This review aims to provide a comprehensive synthesis of current knowledge compiling all known mutations resulting in hereditary polyneuropathies. In addition, it underscores the molecular pathomechanisms of hereditary polyneuropathies and evaluates emerging therapeutic strategies, including adeno-associated virus mediated RNA interference, CRISPR-based gene editing, antisense oligonucleotide therapy, and small-molecule modulators of axonal degeneration. Furthermore, the integration of precision diagnostics, such as next-generation sequencing and functional genomic approaches, is discussed in the context of personalized disease management. Collectively, this review underscores the need for patient-centered approaches in advancing care for individuals with hereditary polyneuropathies.

The major myelin protein expressed by the peripheral nervous system Schwann cells is protein zero (P0), representing 50% of the total protein content in myelin. This 30-kDa integral membrane protein consists of an immunoglobulin (Ig)-like domain, a transmembrane helix, and a 69-residue C-terminal cytoplasmic tail (P0ct). The basic residues in P0ct contribute to the tight packing of the myelin lipid bilayers, and alterations in the tail affect how P0 functions as an adhesion molecule necessary for the stability of compact myelin. Several neurodegenerative neuropathies are related to P0, including the more common Charcot-Marie-Tooth disease (CMT) and Dejerine-Sottas syndrome (DSS), but also rare cases of motor and sensory polyneuropathy. We find that high P0ct concentrations affect the membrane properties of bicelles and induce a lamellar-to-inverted hexagonal phase transition, which causes the bicelles to fuse into long, protein-containing filament-like structures. These structures likely reflect the formation of semi-crystalline lipid domains of potential relevance for myelination. Not only is P0ct important for stacking lipid membranes, but time-lapse fluorescence microscopy shows that it might affect membrane properties during myelination. We further describe recombinant production and low-resolution structural characterization of full-length human P0. Our findings shed light on P0ct effects on membrane properties, and with successful purification of full-length P0, we have new tools to study in vitro the role P0 has in myelin formation and maintenance.

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EGR2 (early growth response 2) is a crucial transcription factor for the myelination of the peripheral nervous system. Mutations in EGR2 are reported to cause a heterogenous spectrum of peripheral neuropathy with wide variation in both severity and age of onset, including demyelinating and axonal forms of Charcot-Marie Tooth (CMT) neuropathy, Dejerine-Sottas neuropathy (DSN/CMT3), and congenital hypomyelinating neuropathy (CHN/CMT4E). Here we report a sporadic de novo EGR2 variant, c.1232A > G (NM_000399.5), causing a missense p.Asp411Gly substitution and discovered through whole-exome sequencing (WES) of the proband. The resultant phenotype is severe demyelinating DSN with onset at two years of age, confirmed through nerve biopsy and electrophysiological examination. In silico analyses showed that the Asp411 residue is evolutionarily conserved, and the p.Asp411Gly variant was predicted to be deleterious by multiple in silico analyses. A luciferase-based reporter assay confirmed the reduced ability of p.Asp411Gly EGR2 to activate a PMP22 (peripheral myelin protein 22) enhancer element compared to wild-type EGR2. This study adds further support to the heterogeneity of EGR2-related peripheral neuropathies and provides strong functional evidence for the pathogenicity of the p.Asp411Gly EGR2 variant.

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Introduction Peripheral neuropathy represents a spectrum of diseases with different etiologies. The most common causes are diabetes, exposure to toxic substances including alcohol and chemotherapeutics, immune-mediated conditions, and gene mutations. A thorough workup including clinical history and examination, nerve conduction studies, and comprehensive laboratory tests is warranted to identify treatable causes. First steps The variability of symptoms allows distinguishing characteristic clinical phenotypes of peripheral neuropathy that should be recognized in order to stratify the diagnostic workup accordingly. Nerve conduction studies are essential to determine the phenotype (axonal versus demyelinating) and severity. Laboratory tests, including genetic testing, CSF examination, nerve imaging, and nerve biopsy, represent additional clinical tests that can be useful in specific clinical scenarios. Comments We propose a flow chart based on five common basic clinical patterns of peripheral neuropathy. Based on these five clinical phenotypes, we suggest differential diagnostic pathways in order to establish the underlying cause. Conclusions The recognition of characteristic clinical phenotypes combined with nerve conduction studies allows pursuing subsequent diagnostic pathways that incorporate nerve conduction studies and additional diagnostic tests. This two-tiered approach promises higher yield and better cost-effectiveness in the diagnostic workup in patients with peripheral neuropathy.

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We identified a de novo mutation in the peripheral myelin protein (PMP22) gene of a patient with Déjérine‐Sottas neuropathy. Single‐stranded conformation analysis of PCR‐amplified DNA fragments showed an additional fragment for exon 1 in the patient, which was absent in the unaffected parents. Sequence analysis showed a de novo point mutation C85→A that results in an amino acid substitution Hisl2Gln in the first transmembrane domain of PMP22. This provides further evidence that sporadic cases of Déjérine‐Sottas neuropathy can be due to dominant single base substitutions.© 1995 wiley‐Liss, Inc.

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Objective: To compare nerve cross-sectional area (CSA) in children with Dejerine-Sottas disease (DSD) to matched healthy controls. Background: DSD is a genetically heterogenous, severe demyelinating hereditary neuropathy characterised by onset in the first two years of life, hypotonia, delayed motor development, and motor nerve conduction velocities of 12 m/sec or less. Nerve ultrasound findings have not previously been described in this disorder. Methods: This cross-sectional, matched, case-control study evaluated differences in nerve CSA measured by peripheral nerve ultrasound in children with DSD compared to healthy controls. CSA of the median, ulnar, tibial and sural nerves of the dominant upper and lower limb were measured. Clinical features were also evaluated. Results: Five children with DSD (aged between two and 12 years) and five age- and gender-matched controls were enrolled. A genetic diagnosis was made in four children, each with mutations in different genes: PMP22, MPZ, PRX and EGR2. Four children were unable to ambulate independently. When grouped as a whole, there was no significant difference in nerve CSA in children with DSD compared to controls. However, individual analysis comparing each child with DSD with their matched control indicated nerve enlargement in three out of five children. The largest increase (five-fold) in nerve CSA was observed in a child with a heterozygous PMP22 point mutation. Nerve CSA was moderately increased in two children - one with a heterozygous mutation in MPZ, and the other with compound heterozygous mutations in PRX. Conclusions: Changes in nerve CSA in children with DSD differ according to the underlying genetic aetiology and reflect the variable pathobiologic processes at play within each genetic subtype. Nerve ultrasound may assist in the clinical and genetic diagnosis of DSD, complementing the current clinical and neurophysiologic phenotyping of DSD subtypes. Larger studies in DSD cohorts are required to confirm these findings. Disclosure: Dr. Yiu has nothing to disclose. Dr. Hobbelink has nothing to disclose. Dr. Ryan has nothing to disclose.

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Hereditary neurological disorders represent a wild group of hereditary illnesses affecting mainly the nervous system, the majority of which have a Mendelian inheritance pattern. Here we present the case of two Moroccan patients each affected by a different hereditary neurological disorder. In the first patient WES analysis revealed the presence of the p.Ser72Leu de novo mutation in the PMP22 gene reported for the first time in Africa, specifically in Morocco. This variant is predicted to be in a mutation "hot-spot" region causing Dejerine-Sottas syndrome called also Charcot-Marie-Tooth type 3. The molecular modeling study suggests an important alteration of hydrogen and hydrophobic interactions between the residue in position 72 of the PMP22 protein and its surrounding amino acids. On the other hand, the p.Ala177Thr mutation on the RNASEH2B gene, responsible of Aicardi-Goutières syndrome 2, was carried in a homozygous state by the second patient descending from a consanguineous family. This mutation is common among the Moroccan population as well as in other North African countries. The present results contributed to a better follow-up of both cases allowing better symptom management with convenient treatments.

Abstract Heterozygous deletions of the gene PMP22 are associated to hereditary neuropathy with liability to pressure palsies (HNPP), a demyelinating neuromuscular disease causing variable transitory focal muscles weakness. Deletions involving both copies of PMP22 cause more severe phenotypes, with early-onset neuropathy and impairment in motor development. We report a patient with a severe early-onset demyelinating neuropathy, caused by two different inherited deletions of PMP22, whose parents had an HNPP. The patient showed neurological signs and delay in motor development but normal intellective abilities. A motor and sensitive conduction study showed severe signs of demyelination, suggestive for Dejerine Sottas Syndrome (DSS). The patient's father had a typical HNPP caused by a heterozygous 17p11.2 deletion, encompassing PMP22. The patient's mother reported no neuropathic symptoms, but in a nerve conduction studies, parents and several relatives showed signs of sensory–motor deficit with focal slowing of conduction at common sites of entrapment. Quantitative analysis of PMP22, performed in our patient by multiplex ligation-dependent probe amplification, revealed a compound heterozygous status with the same deletion of the father and a deletion of PMP22 exon 5, after proved to be inherited from the mother. Therefore, when we face an early-onset, severe form of neuropathy, we have to consider rare forms of hereditary neuropathy caused by homozygous or compound heterozygous mutations in PMP22, even if parents are asymptomatic; an exhaustive family history and an electrodiagnostic study are essential to guide genetic tests and to make a diagnosis.

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Charcot‐Marie‐Tooth disease (CMT) and related inherited peripheral neuropathies, including Dejerine‐Sottas syndrome, congenital hypomyelination, and hereditary neuropathy with liability to pressure palsies (HNPP), are caused by mutations in three myelin genes: PMP22, MPZ and Cx32 (GJB1). The most common mutations are the 1.5 Mb CMT1A tandem duplication on chromosome 17p11.2‐p12 in CMT1 patients and the reciprocal 1.5 Mb deletion in HNPP patients. We performed a mutation screening in 174 unrelated CMT patients and three HNPP families of Russian origin. The unrelated CMT patients included 108 clinically and electrophysiologically diagnosed CMT1 cases, 32 CMT2 cases, and 34 cases with unspecified CMT. Fifty‐nine CMT1A duplications were found, of which 58 belonged to the CMT1 patient group. We found twelve distinct mutations in Cx32, six mutations in MPZ, and two mutations in PMP22. Of these respectively, eight, five, and two lead to a CMT1 phenotype. Eight mutations (Cx32: Ile20Asn/Gly21Ser, Met34Lys, Leu90Val, and Phe193Leu; MPZ: Asp134Gly, Lys138Asn, and Thr139Asn; PMP22: ValSer25‐26del) were not reported previously. Phenotype–genotype correlations were based on nerve conduction velocity studies and mutation type. Hum Mutat 15:340–347, 2000. © 2000 Wiley‐Liss, Inc.

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Missense point mutations in Gas3/PMP22 are responsible for the peripheral neuropathies Charcot-Marie-Tooth 1A and Dejerine Sottas syndrome. These mutations induce protein misfolding with the consequent accumulation of the proteins in the endoplasmic reticulum and the formation of aggresomes. During folding, Gas3/PMP22 associates with the lectin chaperone calnexin. Here, we show that calnexin interacts with the misfolded transmembrane domains of Gas3/PMP22, fused to green fluorescent protein, in a glycan-independent manner. In addition, photobleaching experiments in living cells revealed that Gas3/PMP22-green fluorescent protein mutants are mobile but diffuse at almost half the diffusion coefficient of wild type protein. Our results support emerging models for a glycan-independent chaperone role for calnexin and for the mechanism of retention of misfolded membrane proteins in the endoplasmic reticulum.

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Mutations in the Early‐Growth Response 2 (EGR2) gene cause various hereditary neuropathies, including demyelinating Charcot–Marie‐Tooth (CMT) disease type 1D (CMT1D), congenital hypomyelinating neuropathy type 1 (CHN1), Déjerine–Sottas syndrome (DSS), and axonal CMT (CMT2).

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We examined CMT1A duplication of 17p11.2‐p12, mutations of PMP22, MPZ (P0), GJB1 (Cx32), EGR2 and NEFL genes in 57 Korean families with patients diagnosed as having Charcot‐Marie‐Tooth (CMT) disease. The CMT1A duplication was present in 53.6% of 28 CMT type 1 patients. In the 42 CMT families without CMT1A duplication, 10 pathogenic mutations were found in 9 families. The 10 mutations were not detected in 105 healthy controls. Seven mutations (c.318delT (p.Ala106fs) in PMP22, c.352G>A (p.Asp118Asn), c.449‐1G>T (3′‐splice site), c.706A>G (p.Lys236Glu) in MPZ, c.408T>C (p.Val136Ala), c.502T>C (p.Cys168Arg) in GJB1, and c.1001T>C (p.Leu334Pro) in NEFL) were determined to be novel. The mutation frequencies of PMP22 and MPZ were similar to those found in several European populations, however, it appeared that mutations in GJB1 are less frequent in East Asian CMT patients than in Eur opean patients. We described the identified mutations and phenotype‐genotype correlations based on nerve conduction studies. © 2004 Wiley‐Liss, Inc.

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The myelin protein zero gene (MPZ) maps to chromosome 1q22‐q23 and encodes the most abundant peripheral nerve myelin protein. The Po protein functions as a homophilic adhesion molecule in myelin compaction. Mutations in the MPZ gene are associated with the demyelinating peripheral neuropathies Charcot‐Marie‐Tooth disease type 1B (CMT1B), and the more severe Dejerine‐Sottas syndrome (DSS). We have surveyed a cohort of 70 unrelated patients with demyelinating polyneuropathy for additional mutations in the MPZ gene. The 1.5‐Mb DNA duplication on chromosome 17p11.2‐p12 associated with CMT type 1A (CMT1A) was not present. By DNA heteroduplex analysis, four base mismatches were detected in three exons of MPZ. Nucleotide sequence analysis identified a de novo mutation in MPZ exon 3 that predicts an Ile(135)Thr substitution in a family with clinically severe early‐onset CMT1, and an exon 3 mutation encoding a Gly(137)Ser substitution was identified in a second CMT1 family. Each predicted amino acid substitution resides in the extracellular domain of the Po protein. Heteroduplex analysis did not detect either base change in 104 unrelated controls, indicating that these substitutions are disease‐associated mutations rather than common polymorphisms. In addition, two polymorphic mutations were identified in MPZ exon 5 and exon 6, which do not alter the codons for Gly(200) and Ser(228), respectively. These observations provide further confirmation of the role of MPZ in CMT1B and suggest that MPZ coding region mutations may account for a limited percentage of disease‐causing mutations in nonduplication CMT1 patients. © 1996 Wiley‐Liss, Inc.

Background Myelin protein zero (MPZ) is a critical structural component of myelin in the peripheral nervous system. The MPZ gene is regulated, in part, by the transcription factors SOX10 and EGR2. Mutations in MPZ, SOX10, and EGR2 have been implicated in demyelinating peripheral neuropathies, suggesting that components of this transcriptional network are candidates for harboring disease-causing mutations (or otherwise functional variants) that affect MPZ expression. Methodology We utilized a combination of multi-species sequence comparisons, transcription factor-binding site predictions, targeted human DNA re-sequencing, and in vitro and in vivo enhancer assays to study human non-coding MPZ variants. Principal Findings Our efforts revealed a variant within the first intron of MPZ that resides within a previously described SOX10 binding site is associated with decreased enhancer activity, and alters binding of nuclear proteins. Additionally, the genomic segment harboring this variant directs tissue-relevant reporter gene expression in zebrafish. Conclusions This is the first reported MPZ variant within a cis-acting transcriptional regulatory element. While we were unable to implicate this variant in disease onset, our data suggests that similar non-coding sequences should be screened for mutations in patients with neurological disease. Furthermore, our multi-faceted approach for examining the functional significance of non-coding variants can be readily generalized to study other loci important for myelin structure and function.

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Charcot‐Marie‐Tooth disease (CMT) is a heterogeneous disorder and is traditionally classified into two major types, CMT type 1 (CMT1) and CMT type 2 (CMT2). Most CMT1 patients are associated with the duplication of 17p11.2‐p12 (CMT1A duplication) and small numbers of patients have mutations of the peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ), connexin 32 (Cx32/GJB1), and early growth response 2 (EGR2) genes. Some mutations of MPZ and Cx32 were also associated with the clinical CMT2 phenotype. We constructed denaturing gradient gel electrophoresis (DGGE) analysis as a screening method for PMP22, MPZ, and Cx32 mutations and studied 161 CMT patients without CMT1A duplication. We detected 27 mutations of three genes including 15 novel mutations; six of PMP22, three of MPZ, and six of Cx32. We finally identified 21 causative mutations in 22 unrelated patients and five polymorphic mutations. Eighteen of 22 patients carrying PMP22, MPZ, or Cx32 mutations presented with CMT1 and four of them with MPZ or Cx32 mutations presented with the CMT2 phenotype. DGGE analysis was sensitive for screening for those gene mutations, but causative gene mutation was not identified in many of the Japanese patients with CMT, especially with CMT1. Other candidate genes should be studied to elucidate the genetic basis of Japanese CMT patients. Hum Mutat 20:392–398, 2002. © 2002 Wiley‐Liss, Inc.

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The Egr2/Krox20 transactivator is required for activation of many myelin-associated genes during peripheral nerve myelination by Schwann cells. However, recent work has indicated that Egr2 not only activates genes required for peripheral nerve myelination but may also be involved in gene repression. The NAB (NGFI-A/Egr-binding) corepressors interact with Egr2 and are required for proper coordination of myelin formation. Therefore, NAB proteins could mediate repression of some Egr2 target genes, although direct repression by Egr2 or NAB proteins during myelination has not been demonstrated. To define the physiological role of NAB corepression in gene repression by Egr2, we tested whether the Egr2·NAB complex directly repressed specific target genes. A screen for NAB-regulated genes identified several (including Id2, Id4, and Rad) that declined during the course of peripheral nerve myelination. In vivo chromatin immunoprecipitation analysis of the myelinating sciatic nerve was used to show developmental association of both Egr2 and NAB2 on the Id2, Id4, and Rad promoters as they were repressed during the myelination process. In addition, NAB2 represses transcription by interaction with the chromodomain helicase DNA-binding protein 4 (CHD4) subunit of the nucleosome remodeling and deacetylase chromatin remodeling complex, and we demonstrate that CHD4 occupies NAB-repressed promoters in a developmentally regulated manner in vivo. These results illustrate a novel aspect of genetic regulation of peripheral nerve myelination by showing that Egr2 directly represses genes during myelination in conjunction with NAB corepressors. Furthermore, repression of Id2 was found to augment activation of Mpz (myelin protein zero) expression.

Hereditary motor and sensory neuropathies with early onset are uncommon conditions that include Dejerine-Sottas neuropathy, which begins in infancy, and congenital hypomyelinating neuropathy, which manifests in the early postnatal period. However, these two historically defined disease entities are only small parts of the clinical spectrum. It is well recognized that very early onset hereditary neuropathies are frequently caused by de novo dominant mutations in PMP22, MPZ, and EGR2. In addition, mutations in several other dominant and recessive genes for Charcot-Marie-Tooth disease may lead to similar phenotypes. A 20-year-old boy had complaints of weakness of both lower limbs for 1 year, followed by wasting and foot drop, which subsequently involved the upper limbs. Nerve conduction velocity and electromyography of both lower limbs revealed demyelinating sensory motor polyneuropathy. Histological examination of the sural nerve revealed a nerve trunk with perineural soft tissue, with the nerve bundles being irregular and separated by fibrous tissue bands. The later reveals small perivascular infiltration of chronic inflammatory cells, and no granuloma or AFB is seen. The genetic test of whole exome screening for heriditatory neuropathy showed pathogenic (PM2, PVS, PP5) with a gene impact of (NF2: c.363+1G>T), which is a rare entity in our case study to consider the diagnosis despite negative family history. We highlight this rare disease in young man with a high index of clinical suspicion for its diagnosis. Bangladesh J Medicine 2024; 35: 101-105

Myelin sheath plays important roles in information conduction and nerve injury repair in the peripheral nerve system (PNS). Enhancing comprehension of the structure and components of the myelin sheath in the PNS during development would contribute to a more comprehensive understanding of the developmental and regenerative processes. In this research, the structure of sciatic nerve myelin sheath in C57BL/6 mice from embryonic day 14 (E14) to postnatal 12 months (12M) was observed with transmission electron microscopy. Myelin structure appeared in the sciatic nerve as early as E14, and the number and thickness of myelin lamellar gradually increased with the development until 12M. Transcriptome analysis was performed to show the expressions of myelin‐associated genes and transcriptional factors involved in myelin formation. The genes encoding myelin proteins (Mag, Pmp22, Mpz, Mbp, Cnp and Prx) showed the same expression pattern, peaking at postnatal day 7 (P7) and P28 after birth, whereas the negative regulators of myelination (c‐Jun, Tgfb1, Tnc, Cyr61, Ngf, Egr1, Hgf and Bcl11a) showed an opposite expression pattern. In addition, the expression of myelin‐associated proteins and transcriptional factors was measured by Western blot and immunofluorescence staining. The protein expressions of MAG, PMP22, MPZ, CNPase and PRX increased from E20 to P14. The key transcriptional factor c‐Jun co‐localized with the Schwann cells Marker S100β and decreased after birth, whereas Krox20/Egr2 increased during development. Our data characterized the structure and components of myelin sheath during the early developmental stages, providing insights for further understanding of PNS development.

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We report the frequency, positive rate, and type of mutations in 14 genes (PMP22, GJB1, MPZ, MFN2, SH3TC2, GDAP1, NEFL, LITAF, GARS, HSPB1, FIG4, EGR2, PRX, and RAB7A) associated with Charcot–Marie–Tooth disease (CMT) in a cohort of 17,880 individuals referred to a commercial genetic testing laboratory. Deidentified results from sequencing assays and multiplex ligation‐dependent probe amplification (MLPA) were analyzed including 100,102 Sanger sequencing, 2338 next‐generation sequencing (NGS), and 21,990 MLPA assays. Genetic abnormalities were identified in 18.5% (n = 3312) of all individuals. Testing by Sanger and MLPA (n = 3216) showed that duplications (dup) (56.7%) or deletions (del) (21.9%) in the PMP22 gene accounted for the majority of positive findings followed by mutations in the GJB1 (6.7%), MPZ (5.3%), and MFN2 (4.3%) genes. GJB1 del and mutations in the remaining genes explained 5.3% of the abnormalities. Pathogenic mutations were distributed as follows: missense (70.6%), nonsense (14.3%), frameshift (8.7%), splicing (3.3%), in‐frame deletions/insertions (1.8%), initiator methionine mutations (0.8%), and nonstop changes (0.5%). Mutation frequencies, positive rates, and the types of mutations were similar between tests performed by either Sanger (n = 17,377) or NGS (n = 503). Among patients with a positive genetic finding in a CMT‐related gene, 94.9% were positive in one of four genes (PMP22, GJB1, MPZ, or MFN2).

Hereditary neuropathies may be misdiagnosed with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). A correct diagnosis is crucial for avoiding unnecessary therapies and access genetic counseling. We report on nine patients (seven men, mean age 49.2 ± 16.1) diagnosed with and treated as CIDP, in whom mutations or variants of unknown significance (VUS) in genes associated with hereditary neuropathies were reported. All underwent neurological and neurophysiological examination, eight also cerebrospinal fluid (CSF) analysis. In 4/9, nerve ultrasound and/or MR‐neurography were performed. All the patients complained of progressive upper or lower limbs sensory‐motor symptoms, with heterogeneous disease duration (1‐34 years, mean 8.6 ± 10.8). Neurophysiology showed demyelinating signs in seven patients, mixed findings with predominant axonal damage in two patients. Neuroimaging disclosed diffuse abnormalities at proximal and distal segments. Molecular screening showed PMP22 duplication in two patients, mutations in the MPZ, EGR2, and GJB1 genes were reported in each of the remaining patients. The two patients with mixed neurophysiological findings had p.Val30Met mutation in the transthyretin gene. Two patients had VUS in the MARS and HSPB1 genes. Four patients had partial response to immunomodulant therapies, and CSF and neurophysiological features suggesting an inflammatory condition concomitant with the hereditary neuropathy. Hereditary neuropathy may be misdiagnosed with CIDP. The most common pitfalls are CSF (high protein levels and oligoclonal bands), incorrect interpretation of neurophysiology, and transient benefit from therapies. Neuroimaging may be helpful in cases with atypical presentations or when severe axonal damage complicate the neurophysiological interpretation.

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Missense mutations in 22 genes account for one-quarter of Charcot–Marie–Tooth (CMT) hereditary neuropathies. Myelin Protein Zero (MPZ, P0) mutations produce phenotypes ranging from adult demyelinating (CMT1B) to early onset [Déjérine-Sottas syndrome (DSS) or congenital hypomyelination] to predominantly axonal neuropathy, suggesting gain of function mechanisms. To test this directly, we produced mice in which either the MpzS63C (DSS) or MpzS63del (CMT1B) transgene was inserted randomly, so that the endogenous Mpz alleles could compensate for any loss of mutant P0 function. We show that either mutant allele produces demyelinating neuropathy that mimics the corresponding human disease. However, P0S63C creates a packing defect in the myelin sheath, whereas P0S63del does not arrive to the myelin sheath and is instead retained in the endoplasmic reticulum, where it elicits an unfolded protein response (UPR). This is the first evidence for UPR in association with neuropathy and provides a model to determine whether and how mutant proteins can provoke demyelination from outside of myelin.

Early onset hereditary motor and sensory neuropathies are rare disorders encompassing congenital hypomyelinating neuropathy with disease onset in the direct post-natal period and Dejerine–Sottas neuropathy starting in infancy. The clinical spectrum, however, reaches beyond the boundaries of these two historically defined disease entities. De novo dominant mutations in PMP22, MPZ and EGR2 are known to be a typical cause of very early onset hereditary neuropathies. In addition, mutations in several other dominant and recessive genes for Charcot–Marie–Tooth disease may lead to similar phenotypes. To estimate mutation frequencies and to gain detailed insights into the genetic and phenotypic heterogeneity of early onset hereditary neuropathies, we selected a heterogeneous cohort of 77 unrelated patients who presented with symptoms of peripheral neuropathy within the first year of life. The majority of these patients were isolated in their family. We performed systematic mutation screening by means of direct sequencing of the coding regions of 11 genes: MFN2, PMP22, MPZ, EGR2, GDAP1, NEFL, FGD4, MTMR2, PRX, SBF2 and SH3TC2. In addition, screening for the Charcot–Marie–Tooth type 1A duplication on chromosome 17p11.2-12 was performed. In 35 patients (45%), mutations were identified. Mutations in MPZ, PMP22 and EGR2 were found most frequently in patients presenting with early hypotonia and breathing difficulties. The recessive genes FGD4, PRX, MTMR2, SBF2, SH3TC2 and GDAP1 were mutated in patients presenting with early foot deformities and variable delay in motor milestones after an uneventful neonatal period. Several patients displaying congenital foot deformities but an otherwise normal early development carried the Charcot–Marie–Tooth type 1A duplication. This study clearly illustrates the genetic heterogeneity underlying hereditary neuropathies with infantile onset.

The peripheral myelin protein 22 gene (PMP22), the myelin protein zero gene (MPZ, P0), and the connexin 32 gene (Cx32, GJB1) code for membrane proteins expressed in Schwann cells of the peripheral nervous system (PNS). The early growth response 2 gene (EGR2) encodes a transcription factor that may control myelination in the PNS. Mutations in the respective genes, located on human chromosomes 17p11.2, 1q22‐q23, Xq13.1, and 10q21.1‐q22.1, are associated with several inherited peripheral neuropathies.

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We describe a unique patient who had been diagnosed with inflammatory demyelinating polyneuropathy (CIDP) for 13 years with frequent clear responses to immunotherapies and was finally diagnosed with Charcot-Marie-Tooth disease (CMT) with a rare point mutation in PMP22 (c.320G > A, p.G107D). Some patients diagnosed with young-onset CIDP may have underlying CMT, and extensive genetic testing including point mutations of PMP22 gene is required not to miss the diagnosis.

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Point mutations in the peripheral myelin protein 22 (PMP22) gene have been identified to cause demyelinating Charcot-Marie-Tooth disease (CMT) and hereditary neuropathy with liability to pressure palsy (HNPP). To investigate the mutation spectrum of PMP22 in Han-Chinese population residing in Taiwan, 53 patients with molecularly unassigned demyelinating CMT and 52 patients with HNPP-like neuropathy of unknown genetic causes were screened for PMP22 mutations by Sanger sequencing. Three point mutations were identified in four patients with demyelinating CMT, including c.256 C > T (p.Q86X) in two, and c.310delA (p.I104FfsX7) and c.319 + 1G > A in one each. One PMP22 missense mutation, c.124 T > C (p.C42R), was identified in a patient with HNPP-like neuropathy. The clinical presentations of these mutations vary from mild HNPP-like syndrome to severe infantile-onset demyelinating CMT. In vitro analyses revealed that both PMP22 p.Q86X and p.I104FfsX7 mutations result in truncated PMP22 proteins that are almost totally retained within cytosol, whereas the p.C42R mutation partially impairs cell membrane localization of PMP22 protein. In conclusion, PMP22 point mutations account for 7.5% and 1.9% of demyelinating CMT and HNPP patients with unknown genetic causes, respectively. This study delineates the clinical and molecular features of PMP22 point mutations in Taiwan, and emphasizes their roles in demyelinating CMT or HNPP-like neuropathy.

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Charcot-Marie-Tooth disease with deafness is a clinically distinct entity and is associated with mutations or deletions in several genes including PMP22 gene. Here, we report a large family showing characteristic phenotypes of Charcot-Marie-Tooth type 1A along with deafness in an autosomal dominant fashion. We detected a sequence variation (c.68C>G) co-segregating with the disease phenotype and leading to a T23R missense mutation in PMP22.

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Underexpression, overexpression, and point mutations in peripheral myelin protein 22 (PMP22) cause most cases of Charcot-Marie-Tooth disease (CMTD). While its exact functions remain unclear, PMP22 is clearly essential for formation and maintenance of healthy myelin in the peripheral nervous system. This review explores emerging evidence for roles of PMP22 in cholesterol homeostasis. First, we highlight dysregulation of lipid metabolism in PMP22-based forms of CMTD and recently-discovered interactions between PMP22 and cholesterol biosynthesis machinery. We then examine data that demonstrates PMP22 and cholesterol co-traffic in cells and co-localize in lipid rafts, including how disease-causing PMP22 mutations result in aberrations in cholesterol localization. Finally, we examine roles for interactions between PMP22 and ABCA1 in cholesterol efflux. Together, this emerging body of evidence suggests that PMP22 plays a role in facilitating enhanced cholesterol synthesis and trafficking necessary for production and maintenance of healthy myelin.

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Abnormalities of the peripheral myelin protein 22 (PMP22) gene, including duplication, deletion and point mutations are a major culprit in Type 1 Charcot–Marie–Tooth (CMT) diseases. The complete absence of PMP22 alters cholesterol metabolism in Schwann cells, which likely contributes to myelination deficits. Here, we examined the subcellular trafficking of cholesterol in distinct models of PMP22‐linked neuropathies. In Schwann cells from homozygous Trembler J (TrJ) mice carrying a Leu16Pro mutation, cholesterol was retained with TrJ‐PMP22 in the Golgi, alongside a corresponding reduction in its plasma membrane level. PMP22 overexpression, which models CMT1A caused by gene duplication, triggered cholesterol sequestration to lysosomes, and reduced ATP‐binding cassette transporter‐dependent cholesterol efflux. Conversely, lysosomal targeting of cholesterol by U18666A treatment increased wild type (WT)‐PMP22 levels in lysosomes. Mutagenesis of a cholesterol recognition motif, or CRAC domain, in human PMP22 lead to increased levels of PMP22 in the ER and Golgi compartments, along with higher cytosolic, and lower membrane‐associated cholesterol. Importantly, cholesterol trafficking defects observed in PMP22‐deficient Schwann cells were rescued by WT but not CRAC‐mutant‐PMP22. We also observed that myelination deficits in dorsal root ganglia explants from heterozygous PMP22‐deficient mice were improved by cholesterol supplementation. Collectively, these findings indicate that PMP22 is critical in cholesterol metabolism, and this mechanism is likely a contributing factor in PMP22‐linked hereditary neuropathies. Our results provide a basis for understanding how altered expression of PMP22 impacts cholesterol metabolism.

Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous group of inherited neuropathies. The purpose of this study is to identify the clinical and genetic diversity of peripheral myelin protein 22 (PMP22) in Chinese patients with CMT disease and evaluate their correlations with the clinical manifestations. Using the multiplex ligation-dependent probe amplification (MLPA) technique and Sanger sequencing of PMP22 in a cohort of 465 Chinese families between 2007 and 2019, we identified 137 pedigrees with PMP22 duplications (29.5%), 26 pedigrees with PMP22 deletions (5.6%), and 10 pedigrees with point mutations (2.2%). By comparing our data with the results from other CMT centers in China, we estimate that the frequency of PMP22 mutation in mainland China is ~23.3% (261/1120). We confirmed de novo mutations in 40% (4/10) of PMP22 point mutations. We have also identified two severely affected patients who are compound heterozygotes for recessive PMP22 mutations (novel mutation c.320-1 G>A and R157W mutation) and a 1.5 Mb deletion in 17p11.2-p12, suggesting that c.320-1 G>A might be another recessive allele contributing to DSS in addition to the T118M and R157W mutations. A de novo mutation of S79P in PMP22 was also identified concomitantly with the R94W mutation in mitofusin2 (MFN2). Our study highlights the phenotypic variability associated with PMP22 mutations in mainland China. The results provide valuable insights into the current strategy of genetic testing for CMT disease. NGS technology has increased the potential for efficient detection of variants of unknown significance (VUS) and concurrent causative genes. Greater cooperation between neurologists and molecular biologists is needed in future investigations.

Chaperones, also called heat shock proteins (HSPs), transiently interact with proteins to aid their folding, trafficking, and degradation, thereby directly influencing the transport of newly synthesized molecules. Induction of chaperones provides a potential therapeutic approach for protein misfolding disorders, such as peripheral myelin protein 22 (PMP22)-associated peripheral neuropathies. Cytosolic aggregates of PMP22, linked with a demyelinating Schwann cell phenotype, result in suppression of proteasome activity and activation of proteostatic mechanisms, including the heat shock pathway. Although the beneficial effects of chaperones in preventing the aggregation and improving the trafficking of PMP22 have been repeatedly observed, the requirement for HSP70 in events remains elusive. In this study, we show that activation of the chaperone pathway in fibroblasts from PMP22 duplication-associated Charcot–Marie–Tooth disease type 1A patient with an FDA-approved small molecule increases HSP70 expression and attenuates proteasome dysfunction. Using cells from an HSP70.1/3−/− (inducible HSP70) mouse model, we demonstrate that under proteotoxic stress, this chaperone is critical in preventing the aggregation of PMP22, and this effect is aided by macroautophagy. When examined at steady-state, HSP70 appears to play a minor role in the trafficking of wild-type-PMP22, while it is crucial for preventing the buildup of the aggregation-prone Trembler-J-PMP22. HSP70 aids the processing of Trembler-J-PMP22 through the Golgi and its delivery to lysosomes via Rab7-positive vesicles. Together, these results demonstrate a key role for inducible HSP70 in aiding the processing and hindering the accumulation of misfolded PMP22, which in turn alleviates proteotoxicity within the cells.

Myelination of the peripheral nervous system requires Schwann cells (SC) differentiation into the myelinating phenotype. The peripheral myelin protein-22 (PMP22) is an integral membrane glycoprotein, expressed in SC. It was initially described as a growth arrest-specific (gas3) gene product, up-regulated by serum starvation. PMP22 mutations were pathognomonic for human hereditary peripheral neuropathies, including the Charcot-Marie-Tooth disease (CMT). Trembler-J (TrJ) is a heterozygous mouse model carrying the same pmp22 point mutation as a CMT1E variant. Mutations in lamina genes have been related to a type of peripheral (CMT2B1) or central (autosomal dominant leukodystrophy) neuropathy. We explore the presence of PMP22 and Lamin B1 in Wt and TrJ SC nuclei of sciatic nerves and the colocalization of PMP22 concerning the silent heterochromatin (HC: DAPI-dark counterstaining), the transcriptionally active euchromatin (EC), and the nuclear lamina (H3K4m3 and Lamin B1 immunostaining, respectively). The results revealed that the number of TrJ SC nuclei in sciatic nerves was greater, and the SC volumes were smaller than those of Wt. The myelin protein PMP22 and Lamin B1 were detected in Wt and TrJ SC nuclei and predominantly in peripheral nuclear regions. The level of PMP22 was higher, and those of Lamin B1 lower in TrJ than in Wt mice. The level of PMP22 was higher, and those of Lamin B1 lower in TrJ than in Wt mice. PMP22 colocalized more with Lamin B1 and with the transcriptionally competent EC, than the silent HC with differences between Wt and TrJ genotypes. The results are discussed regarding the probable nuclear role of PMP22 and the relationship with TrJ neuropathy.

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Charcot-Marie-Tooth (CMT) syndrome is the most common progressive human motor and sensory peripheral neuropathy. CMT type 1E is a demyelinating neuropathy affecting Schwann cells due to peripheral-myelin-protein-22 (PMP22) mutations, modelized by Trembler-J mice. Curcumin, a natural polyphenol compound obtained from turmeric (Curcuma longa), exhibits dose- and time-varying antitumor, antioxidant and neuroprotective properties, however, the neurotherapeutic actions of curcumin remain elusive. Here, we propose curcumin as a possible natural treatment capable of enhancing cellular detoxification mechanisms, resulting in an improvement of the neurodegenerative Trembler-J phenotype. Using a refined method for obtaining enriched Schwann cell cultures, we evaluated the neurotherapeutic action of low dose curcumin treatment on the PMP22 expression, and on the chaperones and autophagy/mammalian target of rapamycin (mTOR) pathways in Trembler-J and wild-type genotypes. In wild-type Schwann cells, the action of curcumin resulted in strong stimulation of the chaperone and macroautophagy pathway, whereas the modulation of ribophagy showed a mild effect. However, despite the promising neuroprotective effects for the treatment of neurological diseases, we demonstrate that the action of curcumin in Trembler-J Schwann cells could be impaired due to the irreversible impact of ethanol used as a common curcumin vehicle necessary for administration. These results contribute to expanding our still limited understanding of PMP22 biology in neurobiology and expose the intrinsic lability of the neurodegenerative Trembler-J genotype. Furthermore, they unravel interesting physiological mechanisms of cellular resilience relevant to the pharmacological treatment of the neurodegenerative Tremble J phenotype with curcumin and ethanol. We conclude that the analysis of the effects of the vehicle itself is an essential and inescapable step to comprehensibly assess the effects and full potential of curcumin treatment for therapeutic purposes.

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There is an urgent need for the research of the close and enigmatic relationship between nerve biomechanics and the development of neuropathies. Here we present a research strategy based on the application atomic force and confocal microscopy for simultaneous nerve biomechanics and integrity investigations. Using wild-type and hereditary neuropathy mouse models, we reveal surprising mechanical protection of peripheral nerves. Myelinated peripheral wild-type fibres promptly and fully recover from acute enormous local mechanical compression while maintaining functional and structural integrity. The basal lamina which enwraps each myelinated fibre separately is identified as the major contributor to the striking fibre's resilience and integrity. In contrast, neuropathic fibres lacking the peripheral myelin protein 22 (PMP22), which is closely connected with several hereditary human neuropathies, fail to recover from light compression. Interestingly, the structural arrangement of the basal lamina of Pmp22−/− fibres is significantly altered compared to wild-type fibres. In conclusion, the basal lamina and PMP22 act in concert to contribute to a resilience and integrity of peripheral nerves at the single fibre level. Our findings and the presented technology set the stage for a comprehensive research of the links between nerve biomechanics and neuropathies.

We have generated previously transgenic rats that overexpress peripheral myelin protein 22 (PMP22) in Schwann cells. In the nerves of these animals, Schwann cells have segregated with axons to the normal 1:1 ratio but remain arrested at the promyelinating stage, apparently unable to elaborate myelin sheaths. We have examined gene expression of these dysmyelinating Schwann cells using semiquantitative reverse transcription-PCR and immunofluorescence analysis. Unexpectedly, Schwann cell differentiation appears to proceed normally at the molecular level when monitored by the expression of mRNAs encoding major structural proteins of myelin. Furthermore, an aberrant coexpression of early and late Schwann cell markers was observed. PMP22 itself acquires complex glycosylation, suggesting that trafficking of the myelin protein through the endoplasmic reticulum is not significantly impaired. We suggest that PMP22, when overexpressed, accumulates in a late Golgi–cell membrane compartment and uncouples myelin assembly from the underlying program of Schwann cell differentiation.

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Peripheral myelin protein, 22 kDa (PMP22), is a myelin molecule associated with Schwann cells in peripheral nerves (Snipes, G. J., Suter, U., Welcher, A. A., and Shooter, E. M. (1992) J. Cell Biol. 117, 225-238). Mutations affecting the PMP22 gene have been implicated in the trembler mutation in mice (Suter, U., Welcher, A. A., Ozcelik, T., Snipes, G. J., Kosaras, B., Francke, U., Billings-Gagliardi, S., Sidman, R. L., and Shooter, E. M. (1992) Nature 356, 241-244; Suter, U., Moskow, J. J., Welcher, A. A., Snipes, G. J., Kosaras, B., Sidman, R. L., Buchberg, A. M., and Shooter, E. M. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 4382-4386) and Charcot-Marie-Tooth Disease in humans (Patel, P. I., Roa, B. B., Welcher, A. A., Schoener-Scott, R., Trask, B. J., Pentao, L., Snipes, G. J., Garcia, C. A., Francke, U., Shooter, E. M., Lupski, J. R., and Suter, U. (1992) Nature genet. 1, 159-165). In this report, we have studied PMP22 production in cultured rat Schwann cells. Schwann cells contain a 1.8-kilobase mRNA transcript coding for PMP22, and its production is up-regulated in vitro by forskolin. Metabolic labeling combined with immunoprecipitation methods using antibodies raised against synthetic peptides of PMP22 reveal that Schwann cells generate the protein from an 18-kDa precursor form which is post-translationally modified by N-linked glycosylation. A second molecule (molecular mass, 48 kDa) that reacted with PMP22 antibodies was also detected in Schwann cells but is not related chemically to PMP22 as determined by pulse-chase labeling. Metabolic labeling of rat sciatic nerve and Western blot analyses of purified rat sciatic nerve myelin reveal that deglycosylation of PMP22 gives rise to an 18-kDa protein similar in size to that in Schwann cells. These results indicate that cultured Schwann cells may provide a good model in which to investigate the production and function of PMP22 and to establish the cellular basis for the protein's involvement in inherited peripheral neuropathies.

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PMP22 and MPZ are abundant myelin membrane proteins in Schwann cells. The MPZ adhesion protein holds myelin wraps together across the intraperiod line. PMP22 is a tetraspan protein belonging to the Claudin superfamily. Loss of either MPZ or PMP22 causes severe demyelinating Charcot-Marie-Tooth (CMT) peripheral neuropathy, and duplication of PMP22 causes the most common form of CMT, CMT1A. Yet, the molecular functions provided by PMP22 and how its alteration causes CMT are unknown. Here we find MPZ and PMP22 form a specific complex through interfaces within their transmembrane domains. We also find that the PMP22 A67T patient variant that causes a loss-of-function (Hereditary Neuropathy with Pressure Palsies) phenotype maps to this interface, and blocks MPZ association without affecting localization to the plasma membrane or interactions with other proteins. These data define the molecular basis for the MPZ~PMP22 interaction and indicate this complex fulfills an important function in myelinating cells.

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Charcot–Marie–Tooth disease (CMT) is a neuropathy of the peripheral nervous system that afflicts ∼1:2500 people. The most common form of this disease (CMT1A, 1:4000) is associated with duplication of chromosome fragment 17p11.2-12, which results in a third WT PMP22 allele. In rodent models overexpressing the PMP22 (peripheral myelin protein 22) protein and in dermal fibroblasts from patients with CMT1A, PMP22 aggregates have been observed. This suggests that overexpression of PMP22 under CMT1A conditions overwhelms the endoplasmic reticulum quality control system, leading to formation of cytotoxic aggregates. In this work, we used a single-cell flow-cytometry trafficking assay to quantitatively examine the relationship between PMP22 expression and trafficking efficiency in individual cells. We observed that as expression of WT or disease variants of PMP22 is increased, the amount of intracellular PMP22 increases to a greater extent than the amount of surface-trafficked protein. This was true for both transiently transfected cells and PMP22 stable expressing cells. Our results support the notion that overexpression of PMP22 in CMT1A leads to a disproportionate increase in misfolding and mistrafficking of PMP22, which is likely a contributor to disease pathology and progression.

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Charcot-Marie-Tooth disease type 1A (CMT1A), caused by duplication of the peripheral myelin protein 22 (PMP22) gene, and CMT1B, caused by mutations in myelin protein zero (MPZ) gene, are the two most common forms of demyelinating CMT (CMT1), and no treatments are available for either. Prior studies of the MpzSer63del mouse model of CMT1B have demonstrated that protein misfolding, endoplasmic reticulum (ER) retention and activation of the unfolded protein response (UPR) contributed to the neuropathy. Heterozygous patients with an arginine to cysteine mutation in MPZ (MPZR98C) develop a severe infantile form of CMT1B which is modelled by MpzR98C/ + mice that also show ER stress and an activated UPR. C3-PMP22 mice are considered to effectively model CMT1A. Altered proteostasis, ER stress and activation of the UPR have been demonstrated in mice carrying Pmp22 mutations. To determine whether enabling the ER stress/UPR and readjusting protein homeostasis would effectively treat these models of CMT1B and CMT1A, we administered Sephin1/IFB-088/icerguestat, a UPR modulator which showed efficacy in the MpzS63del model of CMT1B, to heterozygous MpzR98C and C3-PMP22 mice. Mice were analysed by behavioural, neurophysiological, morphological and biochemical measures. Both MpzR98C/ + and C3-PMP22 mice improved in motor function and neurophysiology. Myelination, as demonstrated by g-ratios and myelin thickness, improved in CMT1B and CMT1A mice and markers of UPR activation returned towards wild-type values. Taken together, our results demonstrate the capability of IFB-088 to treat a second mouse model of CMT1B and a mouse model of CMT1A, the most common form of CMT. Given the recent benefits of IFB-088 treatment in amyotrophic lateral sclerosis and multiple sclerosis animal models, these data demonstrate its potential in managing UPR and ER stress for multiple mutations in CMT1 as well as in other neurodegenerative diseases. (Left panel) the accumulation of overexpressed PMP22 or misfolded mutant P0 in the Schwann cell endoplasmic reticulum (ER) leads to overwhelming of the degradative capacity, activation of ER-stress mechanisms, and myelination impairment. (Right panel) by prolonging eIF2α phosphorylation, IFB-088 reduces the amount of newly synthesized proteins entering the ER, allowing the protein quality control systems to better cope with the unfolded/misfolded protein and allowing myelination to progress.

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Mutations in myelin protein zero (MPZ) cause inherited peripheral neuropathies, including Charcot-Marie-Tooth disease (CMT) and Dejerine-Sottas neuropathy. Mutant MPZ proteins have previously been reported to cause CMT via enhanced endoplasmic reticulum (ER) stress and Schwann cell (SC) death, although the pathological mechanisms have not yet been elucidated. In this study, we generated an in vitro model of rat SCs expressing mutant MPZ (MPZ V169fs or R98C) proteins and validated the increase in cell death and ER stress induced by the overexpression of the MPZ mutants. Using this model, we examined the efficacy of 3 different aminosalicylic acids (ASAs; 4-ASA, sodium 4-ASA and 5-ASA) in alleviating pathological phenotypes. FACS analysis indicated that the number of apoptotic rat SCs, RT4 cells, induced by mutant MPZ overexpression was significantly reduced following treatment with each ASA. In particular, treatment with 4-ASA reduced the levels of ER stress markers in RT4 cells induced by V169fs MPZ mutant overexpression and relieved the retention of V169fs mutant proteins in the ER. Additionally, the level of an apoptotic signal mediator (p-JNK) was only decreased in the RT4 cells expressing R98C MPZ mutant protein following treatment with 4-ASA. Although 4-ASA is known as a free radical scavenger, treatment with 4-ASA in the in vitro model did not moderate the level of reactive oxygen species, which was elevated by the expression of mutant MPZ proteins. On the whole, the findings of this study indicate that treatment with 4-ASA reduced the ER stress and SC death caused by 2 different MPZ mutants and suggest that ASA may be a potential therapeutic agent for CMT.

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This study is aimed at describing the findings of high-resolution nerve ultrasound in children with Noonan syndrome (NS) and related disorders experiencing pain in their legs. This retrospective cohort study was conducted in the NS expert center of the Radboud University Medical Center in the Netherlands. Patients were eligible if they were younger than 18 years, clinically and genetically diagnosed with NS or a NS related disorder, and experienced pain in their legs. Anamneses and physical examination were performed in all children. In addition, high-resolution nerve ultrasound was used to assess nerve hypertrophy and, if needed, complemented spinal magnetic resonance imaging was performed. Over a period of 6 months, four children, three with NS and one child with NS with multiple lentigines, who experienced pain of their legs were eligible for inclusion. Muscle weakness was found in two of them. High-resolution nerve ultrasound showed (localized) hypertrophic neuropathy in all patients. One child underwent additional spinal magnetic resonance imaging, which showed profound thickening of the nerve roots and plexus. Conclusion: In the four children included with a NS and related disorders, pain was concomitant with nerve hypertrophy, which suggests an association between these two findings. The use of high-resolution nerve ultrasound and spinal magnetic resonance imaging might result in better understanding of the nature of this pain and the possible association to nerve hypertrophy in patients with NS and related disorders. What is Known: • Children with Noonan syndrome and related disorders may report pain in their legs, which is often interpreted as growing pain. • Some adults with Noonan syndrome and related disorders have hypertrophic neuropathy as a possible cause of neuropathic pain. What is New: • This is the first study using high-resolution nerve ultrasound in children with Noonan syndrome and related disorders experiencing pain in their legs. • Hypertrophic neuropathy was diagnosed as possible cause of pain in four children with Noonan syndrome and related disorders. What is Known: • Children with Noonan syndrome and related disorders may report pain in their legs, which is often interpreted as growing pain. • Some adults with Noonan syndrome and related disorders have hypertrophic neuropathy as a possible cause of neuropathic pain. What is New: • This is the first study using high-resolution nerve ultrasound in children with Noonan syndrome and related disorders experiencing pain in their legs. • Hypertrophic neuropathy was diagnosed as possible cause of pain in four children with Noonan syndrome and related disorders.

Background Hereditary motor and sensory neuropathy, also referred to as Charcot–Marie–Tooth disease (CMT), is most often caused by a duplication of the peripheral myelin protein 22 ( PMP22 ) gene. This duplication causes CMT type 1A (CMT1A). CMT1A rarely occurs in combination with other hereditary neuromuscular disorders. However, such rare genetic coincidences produce a severe phenotype and have been reported in terms of “double trouble” overlapping syndrome. Waardenburg syndrome (WS) is the most common form of a hereditary syndromic deafness. It is primarily characterized by pigmentation anomalies and classified into four major phenotypes. A mutation in the SRY sex determining region Y-box 10 ( SOX10 ) gene causes WS type 2 or 4 and peripheral demyelinating neuropathy, central dysmyelinating leukodystrophy, WS, and Hirschsprung disease. We describe a 11-year-old boy with extreme hypertrophic neuropathy because of a combination of CMT1A and WS type 2. This is the first published case on the co-occurrence of CMT1A and WS type 2. Case presentation The 11-year-old boy presented with motor developmental delay and a deterioration in unstable walking at 6 years of age. In addition, he had congenital hearing loss and heterochromia iridis. The neurological examination revealed weakness in the distal limbs with pes cavus. He was diagnosed with CMT1A by the fluorescence in situ hybridization method. His paternal pedigree had a history of CMT1A. However, no family member had congenital hearing loss. His clinical manifestation was apparently severe than those of his relatives with CMT1A. In addition, a whole-body magnetic resonance neurography revealed an extreme enlargement of his systemic cranial and spinal nerves. Subsequently, a genetic analysis revealed a heterozygous frameshift mutation c.876delT (p.F292Lfs*19) in the SOX10 gene. He was eventually diagnosed with WS type 2. Conclusions We described a patient with a genetically confirmed overlapping diagnoses of CMT1A and WS type 2. The double trouble with the genes created a significant impact on the peripheral nerves system. Severe phenotype in the proband can be attributed to the cumulative effect of mutations in both PMP22 and SOX10 genes, responsible for demyelinating neuropathy.

Localized hypertrophic neuropathy is a rare Schwann cell proliferation that usually affects single nerves from the extremities, and it is of unclear etiology in its pure form. RASopathies are a defined group of genetic diseases with overlapping clinical features, usually secondary to germline mutations in genes encoding either components or regulators of the RAS/MAPK pathway. Herein, we report an 11-year-old boy presenting with café au lait spots and right leg length discrepancy. A fascicular nerve biopsy of the tibial nerve demonstrated a Schwann cell proliferation with prominent onion-bulb formation, satisfying criteria for localized hypertrophic neuropathy. Molecular genetic analysis demonstrated identical KRAS mutations (c38_40dupGCG) in the peripheral nerve lesion and melanocytes from café au lait spots, but not in blood, supporting a diagnosis of a KRAS-mediated rasopathy with mosaicism. Immunohistochemical staining in the peripheral nerve lesion demonstrated strong pERK staining consistent with downstream MAPK pathway activation. This report suggests that at least a subset of localized hypertrophic neuropathies are bonafide, well-differentiated Schwann cell neoplasms developing through oncogenic RAS signaling, which provides new insights into the controversial entity historically known as localized hypertrophic neuropathy.

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The Charcot-Marie-Tooth (CMT) syndrome is also referred to as hereditary motor-sensory neuropathy (HMSN). It is not a single disease but has a multitude of genetic causes. The typical clinical characteristics are distal muscle weakness and atrophy, depressed tendon reflexes, often slow motor NCV, and the frequent finding of other similarly affected relatives. The most common variant of this syndrome is HMSN-I showing autosomal dominant inheritance, markedly slow motor NCV and nerve hypertrophy. One form of HMSN-I is linked to the Duffy locus on chromosome 1. There are numerous other varieties of HMSN including other autosomal dominant conditions such as HMSN-II (with nearly normal motor NCV) and several types of familial amyloid neuropathy (with specific amino acid substitutions in transthyretin); autosomal recessive conditions such as HMSN-III (Déjérine-Sottas hypertrophic neuropathy of childhood) and Refsum's disease (defect of phytanic acid metabolism); and conditions produced by mutations on the X chromosome such as X-linked HMSN, Fabry trihexoside storage disease, and adrenomyeloneuropathy. The known biochemical abnormalities, chromosomal locations, clinical findings and genetic counseling of these disorders are reviewed.

Currently more than 30 genes are known to be responsible for genetically determined neuropathies. Charcot-Marie-Tooth (CMT) disease is the most frequent of these hereditary neuropathies, with a prevalence of 4.7 to 36 per 100 000. In its demyelinating forms (CMT1), approximately 70% of cases are associated with a duplication of the PMP22gene. In its axonal forms (CMT2), 10-20% of the cases may be associated with a mutation of the MFN2gene. For North African patients with recessive transmission, a mutation of the LMNA gene must be sought. It is essential to stress the great variability of the phenotype--clinical, electrophysiological, and histologic--between and within families. A detailed analysis of these criteria, together with consideration of ethnic origin, may guide the search for the causal mutation. Whether the case involves certainly hereditary transmission or a sporadic form, it is desirable to be able to examine the maximum number of the patient's kin, both clinically and electrophysiologically. The forms with recessive transmission usually have a very early onset and are more serious than the dominant forms. The early- and very early-onset forms of CMT are increasingly better distinguished: congenital hypomyelination neuropathy (mutations of PMP22, MPZ or EGR2), or more axonal forms, including SMARD1 (Spinal muscle atrophy with respiratory distress; mutations of IGHMBP2) and EOHMSN (Early-onset hereditary motor and sensory neuropathy; mutations of MFN2). The prevention of cutaneous (ulcerations), bone, and amputation complications is very important in patients with hereditary sensory and autonomic neuropathies, because of the severity of the sensory disorders.

An eleven-month-old baby born out of non-consanguineous parentage presented with history of delayed motor milestones. The weakness was predominantly distal; there was intercostal muscle weakness, generalized hypotonia and areflexia. The nerve conduction velocities were unobtainable in all the four limbs. Sural nerve biopsy was consistent with the diagnosis of congenital hypomyelinating neuropathy, a rare form of hereditary motosensory neuropathy.

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B), chromosome 16 (CMT1C) and chromosome 10 (CMT1D). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-p12. In rare patients it may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (Po or MPZ) gene. Mutations in the SIMPLE gene cause CMT1C, and CMT1D is the result of mutations in the early response 2 (ERG2 or Krox-20) gene. An X-linked form of CMT1 (CMT1X) maps to Xq13 and is associated with mutations in the connexin32 (Cx32) gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy that maps to chromosome 1p35-p36 (CMT2A), chromosome 3q13-q22 (CMT2B), chromosome 7p14 (CMT2D), chromosome 8p21 (CMT2E), chromosome 1q22-q23 (CMT2F) or chromosome 3q13 (CMT2G). Two X-linked forms of CMT2 have been reported (CMT2XA and CMT2XB), but the genes remain unidentified. An area that has recently expanded is the identification of autosomal recessive forms of CMT type 1 and 2. Of the eight recessive forms of CMT1 that have been identified to date, only two have been fully characterized at the molecular level (CMT1 AR B 1 and CMT1 AR D). Point mutations were found in the myotubularin-related protein-2 (MTM2) gene for CMT1 AR B1. CMT1 AR D is the result of point mutations in the N-myc downstream-regulated gene 1 (NDRG1). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene, PO gene, EGR2 gene or the PRX gene (for the recessive form). It shares considerable clinical and pathological features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-p12 that results in reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes that originate from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosome 8q, 10q and 11q.

The demyelinating hereditary motor and sensory neuropathies (HMSN) are a group of inherited progressive neuropathies with markedly decreased nerve conduction velocity and chronic segmental demyelination in the peripheral nerve. Inheritance is autosomal dominant (AD) or autosomal recessive (AR). Autosomal dominant demyelinating HMSN (AD HMSN type I) is genetically heterogeneous and at least three different gene loci have been identified: a locus on chromosome 17 (HMSN Ia), a locus on chromosome 1 (HMSN Ib) and a locus not linked to chromosome 17 or 1 (HMSN nonIa-nonIb). HMSN type Ia is the most common form of AD HMSN. Recently, it has been demonstrated that the HMSN Ia phenotype results either from a duplication of chromosome 17p11.2 or from a point mutation in the peripheral nerve-specific PMP-22 gene which is located in the duplication. Pathology of type Ia is dominated by chronic segmental demyelination with classical onion bulbs. Autosomal recessive demyelinating HMSN shows a broad spectrum of pathological features. The genetic defect or defects are not yet known. On the basis of morphological characteristics we were able to discern four subtypes. Two AR subtypes are clinically and electrophysiologically comparable to AD HMSN type I, namely AR HMSN type I with basal lamina onion bulbs and AR HMSN type I with focally folded myelin. Two AR subtypes with amyelination, respectively or hypomyelination of the peripheral nerves are also more severely affected both clinically and electrophysiologically and could be designated as HMSN type III. A third condition with a HMSN type III phenotype shows mainly classical onion bulbs in peripheral nerves, but the inherited nature of this disorder is uncertain and identical features have been described in steroid-responsive inflammatory demyelinating neuropathy. The morphologically based subtypes of AR demyelinating HMSN may represent different genetic disorders, allelic differences or phenotypic variations.

We studied three patients from two kinships, affected by early onset hereditary motor and sensory neuropathy with probable autosomal recessive inheritance (HMSN type III). Morphological studies of sural nerve biopsies revealed an abnormal myelin proliferation. Two adult patients with long-term follow up, lost ability to walk at 28 and 22 years and showed severe involvement of the cranial nerves. Our observations suggest that "hypermyelination neuropathy" with early onset is a progressive disease with poor long-term prognosis. In one kinship the occurrence of the disease in two sibs of both sexes but not in parents, is consistent with an autosomal recessive inheritance. Familial cases of hypermyelination neuropathy have not been described in previous reports. Morphological aspects of this condition are compared with other forms of hypermyelination neuropathy.

Myelin protein zero (MPZ) is a member of the immunoglobulin gene superfamily with single extracellular, transmembrane and cytoplasmic domains. Homotypic interactions between extracellular domains of MPZ adhere adjacent myelin wraps to each other. MPZ is also necessary for myelin compaction since mice which lack MPZ develop severe dysmyelinating neuropathies in which compaction is dramatically disrupted. MPZ mutations in humans cause the inherited demyelinating neuropathy CMT1B. Some mutations cause the severe neuropathies of infancy designated as Dejerine-Sottas disease, while others cause a 'classical' Charcot-Marie-Tooth (CMT) disease Type 1B (CMT1B) phenotype with normal early milestones but development of disability during the first two decades of life. Still other mutations cause a neuropathy that presents in adults, with normal nerve conduction velocities, designated as a 'CMT2' form of CMT1B. To correlate the phenotype of patients with MPZ mutations with their genotype, we identified and evaluated 13 patients from 12 different families with eight different MPZ mutations. In addition, we re-analysed the clinical data from 64 cases of CMT1B from the literature. Contrary to our expectations, we found that most patients presented with either an early onset neuropathy with signs and symptoms prior to the onset of walking or a late onset neuropathy with signs and symptoms at around age 40 years. Only occasional patients presented with a 'classical' CMT phenotype. Correlation of specific MPZ mutations with their phenotypes demonstrated that addition of either a charged amino acid or altering a cysteine residue in the extracellular domain caused a severe early onset neuropathy. Severe neuropathy was also caused by truncation of the cytoplasmic domain or alteration of an evolutionarily conserved amino acid. Taken together, these data suggest that early onset neuropathy is caused by MPZ mutations that significantly disrupt the tertiary structure of MPZ and thus interfere with MPZ-mediated adhesion and myelin compaction. In contrast, late onset neuropathy is caused by mutations that more subtly alter myelin structure and which probably disrupt Schwann cell-axonal interactions.

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B) and to another unknown autosome (CMT1C). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-12, or in rare patients may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (P0 or MPZ) gene. The molecular defect in CMT1C is unknown. X-linked Charcot-Marie-Tooth neuropathy (CMTX), which has clinical features similar to CMT1, is associated with mutations in the connexin32 gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy, also of undetermined cause. Forms of CMT2 map to chromosome 1p36 (CMT2A), chromosome 3p (CMT2B), chromosome 7p (CMT2D), and to chromosome 8p21 (CMT2E). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset, demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene or the P0 gene and shares considerable clinical and pathologic features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-12 and results from reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes originating from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosomes 8q, 10q, and 11q. Hereditary neuralgic amyotrophy (familial brachial plexus neuropathy) is an autosomal dominant disorder causing painful, recurrent brachial plexopathies and maps to chromosome 17q25.

The nerve sonographic features of Dejerine-Sottas disease (DSD) have not previously been described. This exploratory cross-sectional, matched, case-control study investigated differences in nerve cross-sectional area (CSA) in children with DSD compared to healthy controls and children with Charcot-Marie-Tooth disease type 1A (CMT1A). CSA of the median, ulnar, tibial, and sural nerves was measured by peripheral nerve ultrasound. The mean difference in CSA between children with DSD, controls, and CMT1A was determined individually and within each group. Five children with DSD and five age- and sex-matched controls were enrolled. Data from five age-matched children with CMT1A was also included. Group comparison showed no mean difference in nerve CSA between children with DSD and controls. Individual analysis of each DSD patient with their matched control indicated an increase in nerve CSA in three of the five children. The largest increase was observed in a child with a heterozygous Changes in nerve CSA on ultrasonography in children with DSD differ according to the underlying genetic etiology, confirming the variation in underlying pathobiologic processes and downstream morphological abnormalities of DSD subtypes. Nerve ultrasound may assist in the clinical phenotyping of DSD and act as an adjunct to known distinctive clinical and neurophysiologic findings of DSD subtypes. Larger studies in DSD cohorts are required to confirm these findings.

No abstract

Peripheral myelin protein 22 (PMP22), a membrane glycoprotein, plays a significant role in the formation and/or maintenance of compact myelin in the peripheral nervous system. We studied two pedigrees with Dejerine-Sottas disease and identified two novel mutations in the PMP22 gene: one a 2-bp deletional mutation at nucleotide positions 426 and 427 of exon 4 (this is predicted to alter the reading frame at leucine 80 and thus to lead to frame-shifted translation), and the other a guanine to thymine substitution at nucleotide position 636 leading to a cysteine substitution for glycine 150. Both mutations were located in the putative transmembrane domains reported in many cases of Charcot-Marie-Tooth neuropathy, Dejerine-Sottas disease, and hereditary neuropathy with liability to pressure palsies. The results suggest an important role for the putative transmembrane domains of PMP22 in its function.

Curcumin is the newest therapeutic agent for ameliorating the clinical and neuropathologic phenotype of a mouse model of Déjérine-Sottas disease. We undertook a 12-month dose-escalation safety trial of oral curcumin in a 15-year-old Caucasian girl with Déjérine-Sottas disease (point mutation, Ser72Leu) complicated by severe weakness, scoliosis, and respiratory impairment. The patient received 50 mg/kg/day oral curcumin for the first 4 months and 75 mg/kg/day thereafter, to complete a 12-month trial. Outcome measures included muscle strength, pulmonary function, upper/lower extremity disability, neurophysiologic studies, and health-related quality of life. After 12 months, the patient experienced no adverse events, and reported good compliance. There was little improvement in objective outcome measures. Knee flexion and foot strength increased slightly, but hand and elbow strength decreased. Pulmonary function, hand function, and measures of upper/lower extremity disability were stable or reduced. Her neurophysiologic findings were unchanged. Parent-reported quality of life improved for most domains, especially self-esteem, during the 12 months of treatment. Child-reported quality of life, assessed at the final visit, mirrored these results, with overall feelings of happiness and contentment. Further studies are required to explore the efficacy and safety of curcumin for severe demyelinating neuropathies of infancy and early childhood.

Charcot-Marie-Tooth disease (CMT) was initially described more than 100 years ago by Charcot, Marie, and Tooth. It was only recently, however, that molecular genetic studies of CMT have uncovered the underlying causes of most forms of the diseases. Most cases of CMT1 are associated with a 1.5-Mb tandem duplication in 17p11.2-p12 that encompasses the PMP22 gene. Although many genes may exist in this large duplicated region, PMP22 appears to be the major dosage-sensitive gene. CMT1A is the first autosomal dominant disease associated with a gene dosage effect due to an inherited DNA rearrangement. There is no mutant gene, but instead the disease phenotype results from having 3 copies of a normal gene. Furthermore, these findings suggest that therapeutic intervention in CMT1A duplication patients may be possible by normalizing the amount of PMP22 mRNA levels. Alternatively, CMT1A can be caused by mutations in the PMP22 gene. Other forms of CMT are associated with mutations in the MPZ (CMT1B) and Cx32 (CMTX) genes. Thus, mutations in different genes can cause similar CMT phenotypes. The related but more severe neuropathy, Dejerine-Sottas syndrome (DSS), can also be caused by mutations in the PMP22 and MPZ genes. All 3 genes thus far identified by CMT researchers appear to play an important role in the myelin formation or maintenance of peripheral nerves. CMT1A, CMT1B, CMTX, hereditary neuropathy with liability to pressure palsies (HNPP), and DSS have been called myelin disorders or "myelino-pathies." Other demyelinating forms, CMT1C and CMT-AR, may be caused by mutations of not yet identified myelin genes expressed in Schwann cells. The clinically distinct disease HNPP is caused by a 1.5-Mb deletion in 17p11.2-p12, which spans the same region duplicated in most CMT1A patients. Underexpression of the PMP22 gene causes HNPP just as overexpression of PMP22 causes CMT1A. Thus, 2 different phenotypes can be caused by dosage variations of the same gene. It is apparent that the CMT1A duplication and HNPP deletion are the reciprocal products of a recombination event during meiosis mediated through the CMT1A-REPs. CMT1A and HNPP could be thought of as a "genomic disease" more than single gene disorders. Other genetic disorders may also prove to arise from recombination events mediated by specific chromosomal structural features of the human genome (102). Further studies on the recombination mechanism of CMT and HNPP might reveal the causes of site specific homologous recombination in the human genome. The discovery of the PMP22 gene in the 1.5-Mb CMT1A duplication/HNPP deletion critical region also suggests that the clinical phenotype of chromosome aneuploid syndromes may result from the effect of a small subset of dosage-sensitive genes mapping within the region of aneuploidy. The understanding of the molecular basis of CMT1 and related disorders has allowed accurate DNA diagnosis and genetic counseling of inherited peripheral neuropathies and will make it possible to develop rational strategies for therapy. As several loci for CMT2 have been identified, the genes responsible for CMT2 will most likely be disclosed using positional cloning and candidate gene approaches in the near future.

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B) and to another unknown autosome (CMT1C). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-12, or in rare patients may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (P0 or MPZ) gene. The molecular defect in CMT1C is unknown. X-linked Charcot-Marie-Tooth neuropathy (CMTX), which has clinical features similar to CMT1, is associated with mutations in the connexin32 gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy, also of undetermined cause. One form of CMT2 maps to chromosome 1p36 (CMT2A), another to chromosome 3p (CMT2B) and another to 7p (CMT2D). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene or the P0 gene and shares considerable clinical and pathological features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-12 and results from reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes originating from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosome 8q, 10q and 11q. Hereditary neuralgic amyotrophy (familial brachial plexus neuropathy) is an autosomal dominant disorder causing painful, recurrent brachial plexopathies and maps to chromosome 17q25.

Mutations affecting the peripheral myelin protein 22 (PMP22) gene are associated with inherited motor and sensory neuropathies in mouse (Trembler and Trembler-J) and human (Charcot-Marie-Tooth disease type 1A and Dejerine-Sottas syndrome). Although genetic studies have established a critical role of PMP22 in the formation and/or maintenance of myelin in the peripheral nervous system, the biological function of PMP22 in myelin and in non-myelin forming cells remains largely enigmatic. In this Mini-Review, we will summarize the current knowledge about PMP22 and discuss its hypothetical function(s) in a broad context.

Charcot-Marie-Tooth disease (CMT) is the most common inherited disorder of the peripheral nervous system. The frequency of different CMT genotypes has been estimated in clinic populations, but prevalence data from the general population is lacking. Point mutations in the mitofusin 2 (MFN2) gene has been identified exclusively in Charcot-Marie-Tooth disease type 2 (CMT2), and in a single family with intermediate CMT. MFN2 point mutations are probably the most common cause of CMT2. The CMT phenotype caused by mutation in the myelin protein zero (MPZ) gene varies considerably, from early onset and severe forms to late onset and milder forms. The mechanism is not well understood. The myelin protein zero (P(0) ) mediates adhesion in the spiral wraps of the Schwann cell's myelin sheath. X-linked Charcot-Marie Tooth disease (CMTX) is caused by mutations in the connexin32 (cx32) gene that encodes a polypeptide which is arranged in hexameric array and form gap junctions. Estimate prevalence of CMT. Estimate frequency of Peripheral Myelin Protein 22 (PMP22) duplication and point mutations, insertions and deletions in Cx32, Early growth response 2 (EGR2), MFN2, MPZ, PMP22 and Small integral membrane protein of lysosome/late endosome (SIMPLE) genes. Description of novel mutations in Cx32, MFN2 and MPZ. Description of de novo mutations in MFN2. Our population based genetic epidemiological survey included persons with CMT residing in eastern Akershus County, Norway. The participants were interviewed and examined by one geneticist/neurologist, and classified clinically, neurophysiologically and genetically. Two-hundred and thirty-two consecutive unselected and unrelated CMT families with available DNA from all regions in Norway were included in the MFN2 study. We screened for point mutations in the MFN2 gene. We describe four novel mutations, two in the connexin32 gene and two in the MPZ gene. A total of 245 affected from 116 CMT families from the general population of eastern Akershus county were included in the genetic epidemiological survey. In the general population 1 per 1214 persons (95% CI 1062-1366) has CMT. Charcot-Marie-Tooth disease type 1 (CMT1), CMT2 and intermediate CMT were found in 48.2%, 49.4% and 2.4% of the families, respectively. A mutation in the investigated genes was found in 27.2% of the CMT families and in 28.6% of the affected. The prevalence of the PMP22 duplication and mutations in the Cx32, MPZ and MFN2 genes was found in 13.6%, 6.2%, 1.2%, 6.2% of the families, and in 19.6%, 4.8%, 1.1%, 3.2% of the affected, respectively. None of the families had point mutations, insertions or deletions in the EGR2, PMP22 or SIMPLE genes. Four known and three novel mitofusin 2 (MFN2) point mutations in 8 unrelated Norwegian CMT families were identified. The novel point mutations were not found in 100 healthy controls. This corresponds to 3.4% (8/232) of CMT families having point mutations in MFN2. The phenotypes were compatible with CMT1 in two families, CMT2 in four families, intermediate CMT in one family and distal hereditary motor neuronopathy (dHMN) in one family. A point mutation in the MFN2 gene was found in 2.3% of CMT1, 5.5% of CMT2, 12.5% of intermediate CMT and 6.7% of dHMN families. Two novel missense mutations in the MPZ gene were identified. Family 1 had a c.368G>A (Gly123Asp) transition while family 2 and 3 had a c.103G>A (Asp35Asn) transition. The affected in family 1 had early onset and severe symptoms compatible with Dejerine-Sottas syndrome (DSS), while affected in family 2 and 3 had late onset, milder symptoms and axonal neuropathy compatible with CMT2. Two novel connexin32 mutations that cause early onset X-linked CMT were identified. Family 1 had a deletion c.225delG (R75fsX83) which causes a frameshift and premature stop codon at position 247 while family 2 had a c.536G>A (Cys179Tyr) transition which causes a change of the highly conserved cysteine residue, i.e. disruption of at least one of three disulfide bridges. The mean age at onset was in the first decade and the nerve conduction velocities were in the intermediate range. Charcot-Marie-Tooth disease is the most common inherited neuropathy. At present 47 hereditary neuropathy genes are known, and an examination of all known genes would probably only identify mutations in approximately 50% of those with CMT. Thus, it is likely that at least 30-50 CMT genes are yet to be identified. The identified known and novel point mutations in the MFN2 gene expand the clinical spectrum from CMT2 and intermediate CMT to also include possibly CMT1 and the dHMN phenotypes. Thus, genetic analyses of the MFN2 gene should not be restricted to persons with CMT2. The phenotypic variation caused by different missense mutations in the MPZ gene is likely caused by different conformational changes of the MPZ protein which affects the functional tetramers. Severe changes of the MPZ protein cause dysfunctional tetramers and predominantly uncompacted myelin, i.e. the severe phenotypes congenital hypomyelinating neuropathy and DSS, while milder changes cause the phenotypes CMT1 and CMT2. The two novel mutations in the connexin32 gene are more severe than the majority of previously described mutations possibly due to the severe structural change of the gap junction they encode. Charcot-Marie-Tooth disease is the most common inherited disorder of the peripheral nervous system with an estimated prevalence of 1 in 1214. CMT1 and CMT2 are equally frequent in the general population. The prevalence of PMP22 duplication and of mutations in Cx32, MPZ and MFN2 is 19.6%, 4.8%, 1.1% and 3.2%, respectively. The ratio of probable de novo mutations in CMT families was estimated to be 22.7%. Genotype- phenotype correlations for seven novel mutations in the genes Cx32 (2), MFN2 (3) and MPZ (2) are described. Two novel phenotypes were ascribed to the MFN2 gene, however further studies are needed to confirm that MFN2 mutations can cause CMT1 and dHMN.

Hereditary neuropathies are classified into Charcot-Marie-Tooth disease (CMT), familial amyloid polyneuropathy (FAP), hereditary motor neuropathies (HMN) and hereditary sensory (and autonomic) neuropathies (HSAN). CMTs are furthermore classified into demyelinating neuropathies (CMT1), axonal neuropathies (CMT2) and intermediate form. Duplication of PMP22 (CMT1A) accounts for about 70% of CMT1 and MFN2 mutations account for 25% of CMT2. Genes involved in phosphoinositide regulation cause CMT4; MTMR2 mutation in CMT 4B1 and MTMR13/SBF2 mutation in CMT4B2. In addition to these genes, FIG4, which is a causative gene of pale tremor mouse, is newly identified as a gene for CMT4J. MFN2 and GDAP1 cause CMT2 or CMT4. These genes regulate mitochondrial fusion and fission. Altered axonal mitochondrial transport is suggested as the pathogenesis of the CMT. In animal model with pmp22 duplication, ascorbic acid seems to be effective to prevent disease progression. Nationwide trial of ascorbic acid therapy for CMT1A is now ongoing by the intractable neuropathy study group. Curcumin treatment educes apoptosis of cells that express PMP22 point mutation and partially mitigates the severe neuropathy phenotype of Trembler-J mouse model in a dose-dependent manner. Curcumin treatment may have a potential therapeutic role in CMT with PMP22 point mutation in humans. The high throughput system of diagnosis for CMT has been developed by employing a resequencing array system.

Charcot-Marie-Tooth diseases (CMT) are due to abnormalities of many genes, the most frequent being linked to PMP22 (Peripheral Myelin Protein 22). In the past, only spontaneous genetic anomalies occurring in mouse mutants such as Trembler (Tr) mice were available; more recently, several rodent models have been generated for exploration of the pathophysiological mechanisms underlying these neuropathies. Based on the personal experience of our team, we describe here the pathological hallmarks of most of these animal models and compare them to the pathological features observed in some CMT patient nerves (CMT types 1A and E; hereditary neuropathy with liability to pressure palsies, HNPP). We describe clinical data and detailed pathological analysis mainly by electron microscopy of the sciatic nerves of these animal models conducted in our laboratory; lesions of PMP22 deficient animals (KO and mutated PMP22) and PMP22 overexpressed models are described and compared to ultrastructural anomalies of nerve biopsies from CMT patients due to PMP22 gene anomalies. It is of note that while there are some similarities, there are also significant differences between the lesions in animal models and human cases. Such observations highlight the complex roles played by PMP22 in nerve development. It should be borne in mind that we require additional correlations between animal models of hereditary neuropathies and CMT patients to rationalize the development of efficient drugs.

Charcot-Marie-Tooth disease type 1A is a demyelinating, inherited peripheral neuropathy which is associated with a DNA duplication in chromosome 17p11.2-p12 in over 70% of patients with CMT1A. The CMT1A duplication is not detected cytogenetically, and constitutes a tandem duplication of a 1.5-Mb region of DNA flanked by homologous sequences designated as CMT1A-REP. Detection of the CMT1A duplication by molecular methods is a valuable diagnostic test for the majority of CMT1A cases. This duplication mutation shows stable inheritance through multiple generations, and may also arise as a new mutation in sporadic patients. The CMT1A duplication leads to the disease phenotype apparently through increased dosage of a gene(s) within the duplicated segment. A disease gene associated with CMT1A has been identified in the form of PMP22, which maps within the CMT1A duplication region, and encodes a myelin protein of the peripheral nerve. Point mutations in the PMP22 gene have been identified in CMT1A patients, including one case of a new mutation in PMP22 which coincided with the onset of the disease. Thus, two alternative molecular mechanisms are responsible for CMT1A: DNA duplication leading to increased gene dosage, and point mutation of the PMP22 gene.

The peripheral myelin protein 22 (PMP22) and the epithelial membrane proteins (EMP-1, -2, and -3) comprise a subfamily of small hydrophobic membrane proteins. The putative four-transmembrane domain structure as well as the genomic structure are highly conserved among family members. PMP22 and EMPs are expressed in many tissues, and functions in cell growth, differentiation, and apoptosis have been reported. EMP-1 is highly up-regulated during squamous differentiation and in certain tumors, and a role in tumorigenesis has been proposed. PMP22 is most highly expressed in peripheral nerves, where it is localized in the compact portion of myelin. It plays a crucial role in normal physiological and pathological processes in the peripheral nervous system. Progress in molecular genetics has revealed that genetic alterations in the PMP22 gene, including duplications, deletions, and point mutations, are responsible for several forms of hereditary peripheral neuropathies, including Charcot-Marie-Tooth disease type 1A (CMT1A), Dejerine-Sottas syndrome (DDS), and hereditary neuropathy with liability to pressure palsies (HNPP). The natural mouse mutants Trembler and Trembler-J contain a missense mutation in different hydrophobic domains of PMP22, resulting in demyelination and Schwann cell proliferation. Transgenic mice carrying many copies of the PMP22 gene and PMP22-null mice display a variety of defects in the initial steps of myelination and/or maintenance of myelination, whereas no pathological alterations are detected in other tissues normally expressing PMP22. Further characterization of the interactions of PMP22 and EMPs with other proteins as well as their regulation will provide additional insight into their normal physiological function and their roles in disease and possibly will result in the development of therapeutic tools.

Duplication and deletion of the peripheral myelin protein 22 (PMP22) gene cause Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), respectively, while point mutations or small insertions and deletions (indels) usually cause CMT type 1E (CMT1E) or HNPP. This study was performed to identify PMP22 mutations and to analyze the genotype−phenotype correlation in Korean CMT families. By the application of whole-exome sequencing (WES) and targeted gene panel sequencing (TS), we identified 14 pathogenic or likely pathogenic PMP22 mutations in 21 families out of 850 CMT families who were negative for 17p12 (PMP22) duplication. Most mutations were located in the well-conserved transmembrane domains. Of these, eight mutations were not reported in other populations. High frequencies of de novo mutations were observed, and the mutation sites of c.68C>G and c.215C>T were suggested as the mutational hotspots. Affected individuals showed an early onset-severe phenotype and late onset-mild phenotype, and more than 40% of the CMT1E patients showed hearing loss. Physical and electrophysiological symptoms of the CMT1E patients were more severely damaged than those of CMT1A while similar to CMT1B caused by MPZ mutations. Our results will be useful for the reference data of Korean CMT1E and the molecular diagnosis of CMT1 with or without hearing loss.

To determine whether predicted fork stalling and template switching (FoSTeS) during mitosis deletes exon 4 in peripheral myelin protein 22 KD (PMP22) and causes gain-of-function mutation associated with peripheral neuropathy in a family with Charcot-Marie-Tooth disease type 1E. Two siblings previously reported to have genomic rearrangements predicted to involve exon 4 of Both affected siblings had a sensorimotor dysmyelinating neuropathy with severely slow nerve conduction velocities (<10 m/sec). RT-PCR studies of Schwann cell RNA from one of the siblings demonstrated a complete in-frame deletion of Our results confirm that that FoSTeS-mediated genomic rearrangement produced a deletion of exon 4 of PMP22, resulting in expression of both PMP22 mRNA and protein lacking this sequence. In addition, we provide experimental evidence for endoplasmic reticulum retention of the mutant protein suggesting a gain-of-function mutational mechanism consistent with the observed CMT1E in this family. PMP22Δ4 is another example of a mutated myelin protein that is misfolded and contributes to the pathogenesis of the neuropathy.

Schwann cells, the myelinating cells of the peripheral nervous system, are derived from the neural crest. Once neural crest cells are committed to the Schwann cell fate, they can take on one of two phenotypes to become myelinating or nonmyelinating Schwann cells, a decision that is determined by interactions with axons. The critical step in the differentiation of myelinating Schwann cells is the establishment of a one-to-one relationship with axons, the so-called "promyelinating" stage of Schwann cell development. The transition from the promyelinating to the myelinating stage of development is then accompanied by a number of significant changes in the pattern of gene expression, including the activation of a set of genes encoding myelin structural proteins and lipid biosynthetic enzymes, and the inactivation of a set of genes expressed only in immature or nonmyelinating Schwann cells. These changes are regulated mainly at the transcriptional level and also require continuous interaction between Schwann cells and their axons. Two transcription factors, Krox 20 (EGR2) and Oct 6 (SCIP/Tst1), are necessary for the transition from the promyelinating to the myelinating stage of Schwann cell development. Krox 20, expressed in myelinating but not promyelinating Schwann cells, is absolutely required for this transition, and myelination cannot occur in its absence. Oct 6, expressed mainly in promyelinating Schwann cells and then down-regulated before myelination, is necessary for the correct timing of this transition, since myelination is delayed in its absence. Neither Krox 20 nor Oct 6, however, is required for the initial activation of myelin gene expression. Although the mechanisms of Krox 20 and Oct 6 action during myelination are not known, mutation in Krox 20 has been shown to cause CMT1, further implicating this protein in the pathogenesis of this disease. Identifying the molecular mechanisms of Krox 20 and Oct 6 action will thus be important both for understanding myelination and for designing future treatments for CMT1. Point mutlations in the genes encoding the myelin proteins PMP22 and P0 cause CMT1A without a gene duplication and CMT1B, respectively. Although the clinical and pathological phenotypes of CMT1A and CMT1B are similar, their molecular pathogenesis is quite different. Point mutations in PMP22 alter the trafficking of the protein, so that it accumulates in the endoplasmic reticulum (ER) and intermediate compartment (IC). Mutant PMP22 also sequesters its normal counterpart in the ER, further reducing the amount of PMP22 available for myelin synthesis at the membrane, and accounting, at least in part, for its severe effect on myelination. Mutant PMP22 probably also activates an ER-to-nucleus signal transduction pathway associated with misfolded proteins, which may account for the decrease of myelin gene expression in Schwann cells in Trembler mutant mice. In contrast, absence of expression of the homotypic adhesion molecule, P0, in mice in which the gene has been inactivated, produces a unique pattern of Schwann cell gene expression, demonstrating that P0 plays a regulatory as well as a structural role in myelination. Whether this role is direct, through a P0-mediated adhesion pathway, or indirect, through adhesion pathways mediated by cadherins or integrins, however, remains to be determined. The molecular mechanisms underlying dysmyelination in CMT1 are thus complex, with pleitropic effects on Schwann cell physiology that are determined both by the type of mutation and the protein mutated. Identifying these molecular mechanisms, however, are important both for understanding myelination and for designing future treatments for CMT1. Although demyelination is the hallmark of CMT1, the clinical signs and symptoms of this disease are probably produced by axonal degeneration, not demyelination. (ABSTRACT TRUNCATED)

Peripheral myelin protein (PMP22) is an integral membrane protein that traffics inefficiently even in wild-type (WT) form, with only 20% of the WT protein reaching its final plasma membrane destination in myelinating Schwann cells. Misfolding of PMP22 has been identified as a key factor in multiple peripheral neuropathies, including Charcot-Marie-Tooth disease and Dejerine-Sottas syndrome. While biophysical analyses of disease-associated PMP22 mutants show altered protein stabilities, leading to reduced surface trafficking and loss of PMP22 function, it remains unclear how destabilization of PMP22 mutations causes mistrafficking. Here, native ion mobility-mass spectrometry (IM-MS) is used to compare the gas phase stabilities and abundances for an array of mutant PM22 complexes. We find key differences in the PMP22 mutant stabilities and propensities to form homodimeric complexes. Of particular note, we observe that severely destabilized forms of PMP22 exhibit a higher propensity to dimerize than WT PMP22. Furthermore, we employ lipid raft-mimicking SCOR bicelles to study PMP22 mutants, and find that the differences in dimer abundances are amplified in this medium when compared to micelle-based data, with disease mutants exhibiting up to 4 times more dimer than WT when liberated from SCOR bicelles. We combine our findings with previous cellular data to propose that the formation of PMP22 dimers from destabilized monomers is a key element of PMP22 mistrafficking.

Diabetic peripheral polyneuropathy is associated with decrements in motor/sensory neuron myelination, nerve conduction and muscle function; however, the mechanisms of reduced myelination in diabetes are poorly understood. Chronic elevation of oxidative stress may be one of the potential determinants for demyelination as lipids and proteins are important structural constituents of myelin and highly susceptible to oxidation. The goal of the current study was to determine whether there is a link between protein oxidation/misfolding and demyelination. We chose two distinct models to test our hypothesis: 1) the leptin receptor deficient mouse (dbdb) model of diabetic polyneuropathy and 2) superoxide dismutase 1 knockout (Sod1(-/-) ) mouse model of in vivo oxidative stress. Both experimental models displayed a significant decrement in nerve conduction, increase in tail distal motor latency as well as reduced myelin thickness and fiber/axon diameter. Further biochemical studies demonstrated that oxidative stress is likely to be a potential key player in the demyelination process as both models exhibited significant elevation in protein carbonylation and alterations in protein conformation. Since peripheral myelin protein 22 (PMP22) is a key component of myelin sheath and has been found mutated and aggregated in several peripheral neuropathies, we predicted that an increase in carbonylation and aggregation of PMP22 may be associated with demyelination in dbdb mice. Indeed, PMP22 was found to be carbonylated and aggregated in sciatic nerves of dbdb mice. Sequence-driven hydropathy plot analysis and in vitro oxidation-induced aggregation of purified PMP22 protein supported the premise for oxidation-dependent aggregation of PMP22 in dbdb mice. Collectively, these data strongly suggest for the first time that oxidation-mediated protein misfolding and aggregation of key myelin proteins may be linked to demyelination and reduced nerve conduction in peripheral neuropathies.

The presence of protein aggregates in the nervous system is associated with various pathological conditions, yet their contribution to disease mechanisms is poorly understood. One type of aggregate, the aggresome, accumulates misfolded proteins destined for degradation by the ubiquitin-proteasome pathway. Peripheral myelin protein 22 (PMP22) is a short-lived Schwann cell (SC) protein that forms aggresomes when the proteasome is inhibited or the protein is overexpressed. Duplication, deletion, or point mutations in PMP22 are associated with a host of demyelinating peripheral neuropathies, suggesting that, for normal SC cell function, the levels of PMP22 must be tightly regulated. Therefore, we speculate that mutant, misfolded PMP22 might overload the proteasome and promote aggresome formation. To test this, sciatic nerves of Trembler J (TrJ) neuropathy mice carrying a leucine-to-proline mutation in PMP22 were studied. In TrJ neuropathy nerves, PMP22 has an extended half-life and forms aggresome-like structures that are surrounded by molecular chaperones and lysosomes. On the basis of these characteristics, we hypothesized that PMP22 aggresomes are transitory, linking the proteasomal and lysosomal protein degradation pathways. Here we show that Schwann cells have the ability to eliminate aggresomes by a mechanism that is enhanced when autophagy is activated and is primarily prevented when autophagy is inhibited. This mechanism of aggresome clearance is not unique to peripheral glia, because L fibroblasts were also capable of removing aggresomes. Our results provide evidence for the involvement of the proteasome pathway in TrJ neuropathy and for the role of autophagy in the clearance of aggresomes.

Accumulation of misfolded proteins and alterations in the ubiquitin-proteasome pathway are associated with various neurodegenerative conditions of the CNS and PNS. Aggregates containing ubiquitin and peripheral myelin protein 22 (PMP22) have been observed in the Trembler J mouse model of Charcot-Marie-Tooth disease type 1A demyelinating neuropathy. In these nerves, the turnover rate of the newly synthesized PMP22 is reduced, suggesting proteasome impairment. Here we show evidence of proteasome impairment in Trembler J neuropathy samples compared with wild-type, as measured by reduced degradation of substrate reporters. Proteasome impairment correlates with increased levels of polyubiquitinated proteins, including PMP22, and the recruitment of E1, 20S and 11S to aggresomes formed either spontaneously due to the Trembler J mutation or upon proteasome inhibition. Furthermore, myelin basic protein, an endogenous Schwann cell proteasome substrate, associates with PMP22 aggregates in affected nerves. Together, our data show that in neuropathy nerves, reduced proteasome activity is coupled with the accumulation of ubiquitinated substrates, and the recruitment of proteasomal pathway constituents to aggregates. These results provide novel insights into the mechanism by which altered degradation of Schwann cell proteins may contribute to the pathogenesis of certain PMP22 neuropathies.

The accumulation of misfolded proteins is associated with various neurodegenerative conditions. Mutations in PMP-22 are associated with the human peripheral neuropathy, Charcot-Marie-Tooth Type 1A (CMT1A). PMP-22 is a short-lived 22 kDa glycoprotein, which plays a key role in the maintenance of myelin structure and compaction, highly expressed by Schwann cells. It forms aggregates when the proteasome is inhibited or the protein is mutated. This study reports the application of atomic force microscopy (AFM) as a detector of profound topographical and mechanical changes in Trembler-J mouse (CMT1A animal model). AFM images showed topographical differences in the extracellular matrix and basal lamina organization of Tr-J/+ nerve fibers. The immunocytochemical analysis indicated that PMP-22 protein is associated with type IV collagen (a basal lamina ubiquitous component) in the Tr-J/+ Schwann cell perinuclear region. Changes in mechanical properties of single myelinating Tr-J/+ nerve fibers were investigated, and alterations in cellular stiffness were found. These results might be associated with F-actin cytoskeleton organization in Tr-J/+ nerve fibers. AFM nanoscale imaging focused on topography and mechanical properties of peripheral nerve fibers might provide new insights into the study of peripheral nervous system diseases.

Charcot-Marie-Tooth (CMT) disease is a peripheral neuropathy associated with gene duplication and point mutations in the peripheral myelin protein 22 (

Peripheral myelin protein 22 (PMP22) resides in the plasma membrane and is required for myelin formation in the peripheral nervous system. Many PMP22 mutants accumulate in excess in the endoplasmic reticulum (ER) and lead to the inherited neuropathies of Charcot-Marie-Tooth (CMT) disease. However, the mechanism through which PMP22 mutants accumulate in the ER is unknown. Here, we studied the quality control mechanisms for the PMP22 mutants L16P and G150D, which were originally identified in mice and patients with CMT. We found that the ER-localised ubiquitin ligase Hrd1/SYVN1 mediates ER-associated degradation (ERAD) of PMP22(L16P) and PMP22(G150D), and another ubiquitin ligase, gp78/AMFR, mediates ERAD of PMP22(G150D) as well. We also found that PMP22(L16P), but not PMP22(G150D), is partly released from the ER by loss of Rer1, which is a Golgi-localised sorting receptor for ER retrieval. Rer1 interacts with the wild-type and mutant forms of PMP22. Interestingly, release of PMP22(L16P) from the ER was more prominent with simultaneous knockdown of Rer1 and the ER-localised chaperone calnexin than with the knockdown of each gene. These results suggest that CMT disease-related PMP22(L16P) is trapped in the ER by calnexin-dependent ER retention and Rer1-mediated early Golgi retrieval systems and partly degraded by the Hrd1-mediated ERAD system.

We have previously shown that oral administration of curcumin significantly decreases the percentage of apoptotic Schwann cells and partially mitigates the severe neuropathy phenotype of the Trembler-J (Tr-J) mouse model in a dose-dependent manner. Here we compared the gene expression in sciatic nerves of 2-week-old pups and adult Tr-J with the same age groups of wild-type mice and found a significant increase in gene expression for hypoxia, inflammatory response and heat-shock proteins, the latter specifically the Hsp70 family, in Tr-J mice. We also detected an activation of different branches of unfolded protein responses (UPRs) in Tr-J mice. Administering curcumin results in lower expression of UPR markers suggesting it relieves endoplasmic reticulum (ER) cell stress sensors in sciatic nerves of Tr-J mice while the level of heat-shock proteins stays comparable to untreated Tr-J mice. We further tested if Hsp70 levels could influence the severity of the Tr-J neuropathy. Notably, reduced dosage of the Hsp70 strongly potentiates the severity of the Tr-J neuropathy, though the absence of Hsp70 had little effect in wild-type mice. In aggregate, these data provide further insights into the pathological disease mechanisms caused by myelin gene mutations and further support the exploration of curcumin as a therapeutic approach for selected forms of inherited neuropathy and potentially for other genetic diseases due to ER-retained mutants.

Misfolding of the α-helical membrane protein peripheral myelin protein 22 (PMP22) has been implicated in the pathogenesis of the common neurodegenerative disease known as Charcot-Marie-Tooth disease (CMTD) and also several other related peripheral neuropathies. Emerging evidence suggests that the propensity of PMP22 to misfold in the cell may be due to an intrinsic lack of conformational stability. Therefore, quantitative studies of the conformational equilibrium of PMP22 are needed to gain insight into the molecular basis of CMTD. In this work, we have investigated the folding and unfolding of wild type (WT) human PMP22 in mixed micelles. Both kinetic and thermodynamic measurements demonstrate that the denaturation of PMP22 by n-lauroyl sarcosine (LS) in dodecylphosphocholine (DPC) micelles is reversible. Assessment of the conformational equilibrium indicates that a significant fraction of unfolded PMP22 persists even in the absence of the denaturing detergent. However, we find the stability of PMP22 is increased by glycerol, which facilitates quantitation of thermodynamic parameters. To our knowledge, this work represents the first report of reversible unfolding of a eukaryotic multispan membrane protein. The results indicate that WT PMP22 possesses minimal conformational stability in micelles, which parallels its poor folding efficiency in the endoplasmic reticulum. Folding equilibrium measurements for PMP22 in micelles may provide an approach to assess the effects of cellular metabolites or potential therapeutic agents on its stability. Furthermore, these results pave the way for future investigation of the effects of pathogenic mutations on the conformational equilibrium of PMP22.

Schwann cell-derived peripheral myelin protein-22 (PMP-22) when mutated or overexpressed causes heritable neuropathies with a previously unexplained "gain-of-function" endoplasmic reticulum (ER) retention phenotype. In wild-type sciatic nerves, PMP-22 associates in a specific, transient (t(1/2 ) approximately equal to 11 min), and oligosaccharide processing-dependent manner with the lectin chaperone calnexin (CNX), but not calreticulin nor BiP. In Trembler-J (Tr-J) sciatic nerves, prolonged association of mutant PMP-22 with CNX is found (t(1/2) > 60 min). In 293A cells overexpressing PMP-22(Tr-J), CNX and PMP-22 colocalize in large intracellular structures identified at the electron microscopy level as myelin-like figures with CNX localization in the structures dependent on PMP-22 glucosylation. Similar intracellular myelin-like figures were also present in Schwann cells of sciatic nerves from homozygous Trembler-J mice with no detectable activation of the stress response pathway as deduced from BiP and CHOP expression. Sequestration of CNX in intracellular myelin-like figures may be relevant to the autosomal dominant Charcot-Marie-Tooth-related neuropathies.

The genetical forms of hypertrophic neuropathies, inherited either as recessive or autosomal dominant trait, are classified, according to Dyck (1975), as HMSN type I, III, and IV. Sporadic cases are also reported. We studied three patients, one with autosomal recessive inheritance, and two without family history, who had the following common features: --onset of symptoms before the age to two years; --slowly progressive course; --peroneal muscular atrophy with absent tendon reflexes; --reduction of MCV and SCV; --decreased number of myelinated fibers; --schwannian cell hyperplasia, with onion bulb complexes formation; --absence of aspects of hypomyelination; --increased number of collagen pockets and denervated Schwann-Remak cells or processes. On light microscopy, multilamellated onion bulbs of large size were found in a very high percentage in case 1, while there were either simple in type or in a lower percentage in case 2. In the third, case, onion bulbs were recognized only on electron microscopy. It is known that in the various kinships affected with type I of HMSN, the pathological changes of peripheral nerves differ greatly. Therefore, despite early onset of symptoms and varying degree of severity of nerve changes, all three cases have been classified within the group of HMSN type I. The different severity of nerve damage may suggest the possibility of a genetical heterogeneity in this disorder.

Respiratory distress was the presenting feature in a 4-month-old male infant suffering from Déjérine-Sottas disease, an inherited sensory-motor polyneuropathy. This unusual but potentially benign disorder can be diagnosed upon peripheral nerve biopsy by noting extensive demyelination with "onion bulb" formation. Polyneuropathy should be considered in the differential diagnosis of infantile neuromuscular weakness including or solely involving bulbar and respiratory muscles.

A case is reported of a boy who developed a severe polyneuropathy in early infancy and died of respiratory failure at the age of 18 months. Autopsy revealed almost total lack of myelin sheaths in the cranial, spinal and peripheral nerves. The defect involved the entire peripheral nervous system and was confined to it, central myelination being normal. It is suggested that this case is another example of the condition described by Lyon (1969) and by Kennedy et al. (1971) in which pathological observations were confined to biopsy material. In spite of some similarities between these cases and those of hypertrophic neuropathy reported by Déjerine and Sottas in 1893, they seem to form a distinct sub-group, possibly even a separate entity: infantile polyneuropathy with defective myelination.