Hereditary demyelinating motor and sensory neuropathy

Ascorbic acid for the treatment of Charcot-Marie-Tooth disease

BACKGROUND

Charcot-Marie-Tooth disease (CMT) comprises a large group of different forms of hereditary motor and sensory neuropathy. The molecular basis of several CMT subtypes has been clarified during the last 20 years. Since slowly progressive muscle weakness and sensory disturbances are the main features of these syndromes, treatments aim to improve motor impairment and sensory disturbances to improve abilities. Pharmacological treatment trials in CMT are rare. This review was derived from a Cochrane review, Treatment for Charcot Marie Tooth disease, which will be updated via this review and a forthcoming title, Treatments other than ascorbic acid for Charcot-Marie-Tooth disease.

OBJECTIVES

To assess the effects of ascorbic acid (vitamin C) treatment for CMT.

SEARCH METHODS

On 21 September 2015, we searched the Cochrane Neuromuscular Specialised Register, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and LILACS for randomised controlled trials (RCTs) of treatment for CMT. We also checked clinical trials registries for ongoing studies.

SELECTION CRITERIA

We included RCTs and quasi-RCTs of any ascorbic acid treatment for people with CMT. Where a study aimed to evaluate the treatment of general neuromuscular symptoms of people with peripheral neuropathy including CMT, we included the study if we were able to identify the effect of treatment in the CMT group. We did not include observational studies or case reports of ascorbic acid treatment in people with CMT.

DATA COLLECTION AND ANALYSIS

Two review authors (BG and JB) independently extracted the data and assessed study quality.

MAIN RESULTS

Six RCTs compared the effect of oral ascorbic acid (1 to 4 grams) and placebo treatment in CMT1A. In five trials involving adults with CMT1A, a total of 622 participants received ascorbic acid or placebo. Trials were largely at low risk of bias. There is high-quality evidence that ascorbic acid does not improve the course of CMT1A in adults as measured by the CMT neuropathy score (0 to 36 scale) at 12 months (mean difference (MD) -0.37; 95% confidence intervals (CI) -0.83 to 0.09; five studies; N = 533), or at 24 months (MD -0.21; 95% CI -0.81 to 0.39; three studies; N = 388). Ascorbic acid treatment showed a positive effect on the nine-hole peg test versus placebo (MD -1.16 seconds; 95% CI -1.96 to -0.37), but the clinical significance of this result is probably small. Meta-analyses of other secondary outcome parameters showed no relevant benefit of ascorbic acid. In one trial, 80 children with CMT1A received ascorbic acid or placebo. The trial showed no clinical benefit of ascorbic acid treatment. Adverse effects did not differ in their nature or abundance between ascorbic acid and placebo.

AUTHORS' CONCLUSIONS

High-quality evidence indicates that ascorbic acid does not improve the course of CMT1A in adults in terms of the outcome parameters used. According to low-quality evidence, ascorbic acid does not improve the course of CMT1A in children. However, CMT1A is slowly progressive and the outcome parameters show only small change over time. Longer study durations should be considered, and outcome parameters more sensitive to change over time should be designed and validated for future studies.

A case of cauda equina syndrome in early-onset chronic inflammatory demyelinating polyneuropathy clinically similar to charcot-marie-tooth disease type 1

To present a case of cauda equina syndrome (CES) caused by chronic inflammatory demyelinating polyneuropathy (CIDP) which seemed clinically similar to Charcot-Marie-Tooth disease type1 (CMT1). CIDP is an immune-mediated polyneuropathy, either progressive or relapsing-remitting. It is a non-hereditary disorder characterized by symmetrical motor and sensory deficits. Rarely, spinal nerve roots can be involved, leading to CES by hypertrophic cauda equina. A 34-year-old man presented with low back pain, radicular pain, bilateral lower-extremity weakness, urinary incontinence, and constipation. He had had musculoskeletal deformities, such as hammertoes and pes cavus, since age 10. Lumbar spine magnetic resonance imaging showed diffuse thickening of the cauda equina. Electrophysiological testing showed increased distal latency, conduction blocks, temporal dispersion, and severe nerve conduction velocity slowing (3 m/s). We were not able to find genetic mutations at the PMP 22, MPZ, PRX, and EGR2 genes. The pathologic findings of the sural nerve biopsy revealed thinly myelinated nerve fibers with Schwann cells proliferation. We performed a decompressive laminectomy, intravenous IgG (IV-IgG) and oral steroid. At 1 week after surgery, most of his symptoms showed marked improvements except foot deformities. There was no relapse or aggravation of disease for 3 years. We diagnosed the case as an early-onset CIDP with cauda equine syndrome, whose initial clinical findings were similar to those of CMT1, and successfully managed with decompressive laminectomy, IV-IgG and oral steroid.

Treatment for Charcot-Marie-Tooth disease

BACKGROUND

Charcot-Marie-Tooth disease (CMT) comprises a large variety of different forms of motor and sensory neuropathies. The most frequent are demyelinating forms (CMT1) and axonal forms (CMT2). The molecular basis of several CMT forms has been clarified during the last 15 years. Since muscle wasting and sensory disturbance are the main features of these syndromes, treatments aim to improve motor impairment and sensory disturbances. Specific treatment trials are rare.

OBJECTIVES

The objective was to review systematically all randomised and quasi-randomised studies of any treatment for CMT.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Trials Register, MEDLINE (January 1966 to August 2007), EMBASE (January 1980 to August 2007), LILACS (January 1982 to August 2007) for randomised controlled trials of treatment for CMT.

SELECTION CRITERIA

We included randomised and quasi-randomised trials of any treatment for people with CMT. Where a study aimed to evaluate the treatment of general neuromuscular symptoms of people with peripheral neuropathy including CMT, we included the study if we were able to identify the effect of treatment in the CMT group. Observational studies and case reports on the treatment of people with CMT were not included.

DATA COLLECTION AND ANALYSIS

Two review authors (PY and TBB) extracted the data, assessed study quality and performed data extraction independently.

MAIN RESULTS

Only one trial with only eight participants met all the inclusion criteria and provided the primary outcome measure for this review. In this trial, four participants treated with neurotrophin-3 had more improvement after six months on the Neuropathy Impairment Score, mean difference -9.50 (95% CI -13.77 to -5.23), than those four treated with placebo. Small trials of exercise training, creatine monohydrate, orthoses and purified bovine brain ganglioside injections (Cronassial) showed no significant benefit in people with genetically undefined CMT1 or CMT2.

AUTHORS' CONCLUSIONS

Small trials of exercise, creatine, purified brain gangliosides, and orthoses have been performed. None showed significant benefit. A very small trial of neurotrophin-3 showed possible minor benefit which needs to be replicated in a larger trial. None of the two trials were large enough to detect moderate benefit or harm. Larger RCTs are needed for any form of pharmacological intervention as well as as for any form of physical intervention. Outcome measures should include a validated composite scale such as the Charcot-Marie-Tooth neuropathy scale.

Charcot-Marie-Tooth type 4B demyelinating neuropathy: deciphering the role of MTMR phosphatases

Charcot-Marie-Tooth type 4B (CMT4B) is a severe autosomal recessive neuropathy with demyelination and myelin outfoldings of the nerve. This disorder is genetically heterogeneous, but thus far, mutations in myotubularin-related 2 (MTMR2) and MTMR13 genes have been shown to underlie CMT4B1 and CMT4B2, respectively. MTMR2 and MTMR13 belong to a family of ubiquitously expressed proteins sharing homology with protein tyrosine phosphatases (PTPs). The MTMR family, which has 14 members in humans, comprises catalytically active proteins, such as MTMR2, and catalytically inactive proteins, such as MTMR13. Despite their homology with PTPs, catalytically active MTMR phosphatases dephosphorylate both PtdIns3P and PtdIns(3,5)P2 phosphoinositides. Thus, MTMR2 and MTMR13 may regulate vesicular trafficking in Schwann cells. Loss of these proteins could lead to uncontrolled folding of myelin and, ultimately, to CMT4B. In this review, we discuss recent findings on this interesting protein family with the main focus on MTMR2 and MTMR13 and their involvement in the biology of Schwann cell and CMT4B neuropathies.

Spastic paraplegia, optic atrophy, and neuropathy is linked to chromosome 11q13

We report an autosomal recessive neurodegenerative disorder in 25 white members from a large inbred Brazilian family, 22 of whom were evaluated clinically. This condition is characterized by (1) subnormal vision secondary to apparently nonprogressive congenital optic atrophy; (2) onset of progressive spastic paraplegia in infancy; (3) onset of progressive motor and sensory axonal neuropathy in late childhood/early adolescence; (4) dysarthria starting in the third decade of life; (5) exacerbated acoustic startle response; and (6) progressive joint contractures and spine deformities. Motor handicap was severe, and all patients were wheelchair bound after 15 years old. We performed a genome-wide screen including 25 affected individuals and 49 of their unaffected relatives. Linkage was detected at 11q13 region with a maximum logarithm of odds score of +14.43, obtained with marker D11S1883. The candidate region, which lies between D11S1908 and D11S1889, encompasses approximately 4.8Mb and has more than 100 genes and expressed sequences. We propose the acronym SPOAN (spastic paraplegia, optic atrophy, and neuropathy) for this complex syndrome.

A novel stop codon mutation in the PMP22 gene associated with a variable phenotype

The most frequent inherited peripheral neuropathy is the peripheral myelin protein 22 (PMP22) gene related disease. Duplication, deletion, and point mutations in that gene are associated with phenotypic variability. Here we report a family carrying a novel mutation in the PMP22 gene (c. 327C>A), which results in a premature stop codon (Cys109stop). The family members who carry this mutation have a Charcot-Marie-Tooth type 1 variable phenotype, ranging from asymptomatic to severely affected. These findings suggest that the fourth transmembrane domain of the PMP22 gene may play an important role, although the intrafamilial clinical variability reinforces the observation that pathogenic mutations are not always phenotype determinant and that other factors (genetic or epigenetic) modulate the severity of the clinical course.

Dejerine-Sottas disease and hereditary demyelinating polyneuropathy of infancy

Dejerine-Sottas disease (DSD) was originally described as a hypertrophic polyneuropathy characterized by onset in infancy or early childhood in patients born to unaffected parents. The clinical features included distal sensory changes with ataxia; pes cavus, at times with kyphoscoliosis; motor deficit and atrophy predominating in the distal lower limbs and progressing toward the proximal limbs following a length-dependent pattern; palpable nerve hypertrophy; and Argyll-Robertson pupils. The morphological hallmark was the extensive nerve and root hypertrophy associated with demyelination-remyelination of surviving, originally myelinated axons and profuse Schwann-cell proliferation forming onion bulbs. Wide variations in clinical manifestations of chronic demyelinating polyneuropathies of early onset in children born to unaffected parents have now been reported, with only some of the characteristics required in the original study, and at least seven genes encoding the myelin proteins P0, PMP22, the transcriptional factor EGR2, and others have been implicated. Thus, DSD is now a component of the hereditary demyelinating polyneuropathies of infancy that also include subsets of the recently individualized CMT4 neuropathies. The presumed recessive transmission of patients with DSD should be confirmed by molecular genetic analysis, which is still negative in a significant proportion of patients. The nerve biopsy can be useful in patients in whom genealogical or DNA abnormalities in favor of a genetic disorder are missing, because in a few patients with a progressive or relapsing course the diagnosis of early-onset chronic inflammatory demyelinating polyneuropathy must be considered.

Dejerine-Sottas syndrome grown to maturity: overview of genetic and morphological heterogeneity and follow-up of 25 patients

Dejerine-Sottas syndrome (DSS) is an early onset demyelinating motor and sensory neuropathy with motor nerve conduction velocities below 12 m s(-1). The phenotype is genetically heterogeneous, and autosomal dominant (AD) as well as autosomal recessive (AR) inheritance is described. Nerve pathology is highly variable. It is generally presumed that clinical course is severe, leading to wheelchair dependency at an early age. In this study we documented the clinical and pathological features in 25 patients with a DSS and we evaluated the clinical course. In our series 14 patients had an AD mutation and six were probably affected by an AR disorder. In three patients inheritance mode was unknown and two patients obviously suffered from an acquired disorder. The clinical course in all patients was documented. Nine of the 25 patients showed a moderate handicap in adult life; walking distance was still at least 1 km. Age at last investigation of the ambulant patients ranged from 22 to 62 years (mean 38.6 years), and ambulant patients were found in all genetic subgroups. We conclude that DSS, although in general denoting a more serious neuropathy than CMT1, does not imply a severe disability or wheelchair dependency in adult life.

Characterisation of autoantibodies to peripheral myelin protein 22 in patients with hereditary and acquired neuropathies

To investigate the possibility that an autoimmune mechanism may play a role in the hereditary neuropathy Charcot-Marie-Tooth type 1A (CMT1A), sera were analysed by Western blot for anti-peripheral myelin protein 22 (PMP22) autoantibodies. These sera were compared with sera from patients with CMT type 2 (CMT2), acquired peripheral neuropathies such as chronic inflammatory demyelinating neuropathy (CIDP), anti-MAG IgM neuropathy, Miller-Fisher syndrome (MFS), diabetic neuropathy and with control blood donors. Anti-PMP22 positive sera were detected in 70% of patients with CMT1 and unexpectedly in 60% of patients with CMT2. Interestingly, 44% of the patients with other peripheral neuropathies and 23% of the apparently healthy controls showed also anti-PMP22 antibody reactivity. Immunohistochemical analysis of the human anti-PMP22 antisera on healthy sural nerve sections and on PMP22-expressing COS cells revealed that these sera did not recognise endogenous PMP22. Our results indicate that anti-PMP22 autoantibodies are found in sera of patients with different types of peripheral neuropathies, but their role in the pathogenesis of these diseases remains to be determined.

Autosomal recessive hereditary neuropathy with focally folded myelin sheaths and linked to chromosome 11q23: a distinct and homogeneous entity

We describe a six generation Saudi kindred, with a recessive hereditary motor and sensory neuropathy (HMSN). Four individuals were affected including two children (a boy and a girl) and a 23-year-old man. The fourth (a female) died at the age of 14 years. Onset of the disease was early (< 2 years) and the clinical and neurophysiological features were, generally, quite similar to those of an Italian family linked to chromosome 11q23. The peculiar pathologic pattern was irregular and redundant loops associated with folding of the myelin sheaths. The genetic study confirmed linkage to chromosome 11q23 and refined the location of the gene between D11S1311 and D11S917, a 3.3 cM region. These findings support the existence of a homogeneous and distinct entity within the form of HMSN associated with focally folded myelin sheaths.

Charcot-marie-tooth disease and related neuropathies: molecular basis for distinction and diagnosis

Great advances have been made in understanding the molecular basis of Charcot-Marie-Tooth disease (CMT) and related neuropathies, namely Dejerine-Sottas disease (DSD), hereditary neuropathy with liability to pressure palsies (HNPP) and congenital hypomyelination (CH). The number of newly uncovered mutations and identified genetic loci is rapidly increasing, and, as a consequence, the classification of these disorders is becoming more complicated. Molecular genetics, animal models, and transfected cell studies are shedding light on function and dysfunction of proteins involved in hereditary myelinopathies-peripheral myelin protein 22 (PMP22), myelin protein zero (PO), connexin 32 (Cx32), and early growth response 2 (EGR2). Gene dosage effect, loss of function, gain of toxic function, and dominant negative effect are possible mechanisms whereby different gene mutations may exert their detrimental action on peripheral nerves. A tentative rational approach to clinical and molecular diagnosis based on genotype-phenotype correlation analysis is described.

Recessive inheritance of a new point mutation of the PMP22 gene in Dejerine-Sottas disease

The existence of recessive transmission of Dejerine-Sottas disease, a severe demyelinating neuropathy of childhood, has been questioned, because only heterozygous mutations of the myelin proteins P0 or PMP22 genes have been identified in virtually all patients with this phenotype. We report on a family with 3 affected children with this phenotype, born to clinically and electrophysiologically unaffected parents. All 3 children carried a previously unknown homozygous missense point mutation (Arg157Trp) of the PMP22 gene. The parents were heterozygous for the same mutation. These findings demonstrate the occurrence of recessive transmission in this setting.

A small direct tandem duplication of the myelin protein zero gene in a patient with Dejerine-Sottas disease phenotype

We present a male patient with Dejerine-Sottas disease phenotype, who had a small direct tandem duplication of the Po gene. The pathology of the sural nerve showed hypomyelinated fibers with absence of active demyelination and onion-bulb formations composed of two parallel layers of basement membrane, consistent with congenital hypomyelination neuropathy (CHN). However, his clinical features were more severe than those of previously reported CHN patients. A GGCA insertion was identified at the position of nucleotide 560 in the myelin protein zero (Po) gene. This insertional mutation was located in exon 4 coding for the transmembrane domain of the Po gene and caused a shift of reading frame, creating a stop codon. The mutation of the transmembrane domain probably has the largest impact on Po function. The mutation was not identified in both parents.

Tomaculous neuropathy in Charcot-Marie-Tooth disease with myelin protein zero gene mutation

Mutation of the myelin protein zero (MPZ) gene is associated with a small number of Charcot-Marie-Tooth (CMT) patients. We present a patient with Lys 130 Arg substitution in the extracellular domain who showed tomacula formation in biopsied sural nerve. CMT patients with mutations Ly 96 Glu, Lys 130 Arg and Ile 135 Leu showed tomaculous neuropathy. Present and previously reported investigations suggest that the pathological phenotypes of peripheral nerve are probably related to the mutations of the MPZ gene.

An in-frame deletion in peripheral myelin protein-22 gene causes hypomyelination and cell death of the Schwann cells in the new Trembler mutant mice

Cloning and sequencing of the peripheral myelin protein-22 cDNA and genomic DNA from newly found Trembler mice revealed an in-frame deletion including exon IV which codes for the second (TM2) and a part of third (TM3) transmembrane domain of peripheral myelin protein-22. This mutation was distinct from those in both other allelic Trembler and Trembler-J mice, which carry point mutations within the putative transmembrane spanning regions of peripheral myelin protein-22. Inheritance was autosomal dominant. The affected mice revealed an abnormal gait, which appeared at 15-20 days of age, followed by motor and sensory ataxia, which remained throughout life. Most of the affected mice could survive more than one year. One of the most notable pathological phenotypes was a giant vacuolar formation in the sciatic nerve of homozygotes. They vary in size within the cytoplasm of Schwann cells, which failed to assemble myelin at any ages studied. Heterozygotes showed normal myelination during the early postnatal stages, followed by a segmental demyelination at an advanced stage. Vacuolar formation was not so frequent as in the homozygotes. These results suggest that the missing of transmembrane spanning region (TM2 and TM3) of peripheral myelin protein-22 may disturb a dual biological function of peripheral myelin protein-22, leading to a dysmyelination of axons and to a vacuolar formation within the cytoplasm of the Schwann cells. The latter phenotype is discussed in conjunction with the disruption of an intracellular transport system and subsequent cell death.

Abnormal Schwann cell/axon interactions in the Trembler-J mouse

The Trembler-J (TrJ) mouse has a point mutation in the gene coding for peripheral myelin protein 22 (PMP22). Disturbances in PMP22 are associated with abnormal myelination in a range of inherited peripheral neuropathies both in mice and humans. PMP22 is produced mainly by Schwann cells in the peripheral nervous system where it is localised to compact myelin. The function of PMP22 is unclear but its low abundance (approximately 5% of total myelin protein) means that it is unlikely to play a structural role. Its inclusion in a recently discovered family of proteins suggests a function in cell proliferation/differentiation and possibly in adhesion. Nerves from TrJ and the allelic Trembler (Tr) mouse are characterised by abnormally thin myelin for the size of the axon and an increased number of Schwann cells. We report ultrastructural evidence of abnormal Schwann cell-axon interactions. Schwann cell nuclei have been found adjacent to the nodes of Ranvier whereas in normal animals they are located near the centre of the internodes. In some fibres the terminal myelin loops faced outwards into the extracellular space instead of turning inwards and terminating on the axon. In severely affected nerves many axons were only partially surrounded by Schwann cell cytoplasm. All these features suggest a failure of Schwann cell-axon recognition or interaction. In addition to abnormalities related to abnormal myelination there was significant axonal loss in the dorsal roots.

Unexpected recovery in a newborn with severe hypomyelinating neuropathy

We report the case of a severely hypotonic and weak term newborn who required ventilatory support from the time of birth. Serial neurophysiologic studies were consistent with severe demyelinating polyneuropathy. The infant's condition deteriorated over several weeks despite treatment with corticosteroids and intravenous immunoglobulin (IVIG) for presumed inflammatory demyelinating polyneuropathy. Histopathologic findings in a sural nerve biopsy, however, were similar to those previously reported in congenital hypomyelinating neuropathies. After 12 weeks of hospitalization and after discontinuation of corticosteroids, the patient began to recover and required no further ventilatory support. Remarkable improvement has continued for 18 months. This patient raises questions about the underlying mechanisms of hypomyelinating neuropathies in early infancy.

The pathology of charcot-marie-tooth disease and related disorders

Approximately a quarter of a century ago, the disorders originally designated as Charcot-Marie-Tooth disease and Dejerine-Sottas disease were shown by combined clinical, electrophysiological and nerve biopsy studies to be genetically complex. In pathological terms they could be broadly classified into demyelinating neuropathies and axonopathies. Advances in the molecular genetics of these disorders, particularly for those with a demyelinating basis, have recently produced substantial new insights. The identification of mutations in genes for myelin proteins has provided the opportunity for investigating the precise mechanisms of these neuropathies, including the use of spontaneous and genetically engineered animal models.

Hereditary neuropathies in children: the contribution of the new genetics

Although the prevalence of the hereditary motor and sensory neuropathies in childhood is not clearly established and the age of presentation may overlap the arbitrary boundary between pediatric and adult neurology, the recent explosion of genetic information regarding these conditions has completely altered our understanding and classification of these diseases. The current status of our understanding of the molecular basis of the hereditary neuropathies which might present in childhood is reviewed. The impact of this information on our concepts of the mechanisms operative in the production of the clinical signs and symptoms in these diseases is discussed.

Correlation between the histopathologic, genotypic, and phenotypic features of hereditary peripheral neuropathies in childhood

In recent years, there have been remarkable advances in the understanding of the molecular genetic basis of the hereditary polyneuropathies. Linkage of the genes for Charcot-Marie-Tooth disease to chromosomes 1 and then 17 was followed by the discovery that the commonest form of Charcot-Marie-Tooth disease (CMT1A) was due to a duplication of DNA at 17p11.2-12. This duplication was shown to contain the gene for peripheral myelin protein PMP22. The finding that mutations of the myelin protein PMP22 gene were present in some Charcot-Marie-Tooth disease cases lacking the duplication confirmed the myelin protein PMP22 gene as the site of the defect in Charcot-Marie-Tooth disease. Similarly, defects of the myelin protein P0 gene on chromosome 1 have been demonstrated in a rarer form of Charcot-Marie-Tooth disease (CMT1B). A deletion of DNA at 17p11.2-12 results in the disorder hereditary neuropathy with liability to pressure palsies. Other mutations of the myelin protein PMP22 and myelin protein P0 genes have been associated with the clinical syndrome known as Dejerine-Sottas disease. An X-linked form of Charcot-Marie-Tooth disease (CMTX) has been characterized and shown to be due to mutations of the gap junction protein, connexin 32. Transgenic murine models with inactivated myelin protein PMP22 and myelin protein P0 genes have shown pathologic changes strinkingly similar to those seen in human patients with disturbances of those genes. In this paper, the clinical and histopathologic characteristics of these conditions are discussed in relation to the genotypic basis. It will be argued that there is still an important place for the clinician and nerve pathologist in a medical world immersed in the wonders of molecular genetics.

MRI of peripheral nerves and pathology of sural nerves in hereditary motor and sensory neuropathy type III

We investigated two patients with hereditary motor and sensory neuropathy type III, one with Déjérine-Sottas disease and the other with congenital hypomyelination neuropathy based on nerve pathology and MRI of the sciatic nerve. On biopsy of the sural nerve of the patient with Déjérine-Sottas disease, myelin debris, indicating demyelination, was observed in an onion-bulb pattern surrounding myelinated fibres. In the patient with congenital hypomyelination neuropathy, onion bulbs were formed of two parallel layers of basement membrane. There was no evidence of myelin breakdown. On axial T2-weighted MRI, a severely hypertropied sciatic nerve containing multiple rounded lesions, suggesting inflammation or demyelination, was observed in the patient with Déjérine-Sottas disease. In contrast, the sciatic nerve of the patient with congenital hypomyelination neuropathy showed slight hypertrophy without demyelination. MRI of the sciatic nerve may represent a useful tool for characterisation of demyelinating disease and its prognosis.

Molecular analysis of three cases with hereditary motor and sensory neuropathy with myelin outfolding

We describe three patients affected by a congenital motor and sensory neuropathy with excessive myelin outfoldings (MOs) [15]. Clinical and electrophysiological features supported the diagnosis of hereditary motor and sensory neuropathy. We previously reported a genetic study on these three patients, which failed to demonstrate either the duplication in chromosome 17p11.2 or the mutations at exons 1 and 2 of the peripheral myelin protein gene (PMP-22) and suggested an autosomal recessive (AR) inheritance. In this study we described the absence of the most common mutations, which characterized other forms of hereditary motor and sensory neuropathy (HMSN). In particular the absence of molecular changes in the PMP-22 gene definitively sets HMSN with MOs apart from the more common CMT1A, hereditary neuropathy with liability to pressure palsies (HNPP) and progressive sensory-motor polyneuropathy with tomaculous changes at sural nerve biopsy.

Molecular basis of common hereditary motor and sensory neuropathies in humans and in mouse models

The Hereditary Motor and Sensory Neuropathies (HMSNs) are well known to be clinically, morphologically, and genetically heterogeneous. Yet, recent advances in the cellular and molecular biology of the peripheral nervous system coupled with remarkable progress in human and mouse genetics have provided a framework that has profoundly changed our understanding of the pathogenesis of these diseases. It now appears that most of the HMSNs are related to mutations affecting genes encoding Schwann cell proteins, specifically the Peripheral Myelin Protein PMP22, Myelin Protein Zero, and one of the gap junction proteins, connexin-32. Accordingly, these findings are discussed in the context of the clinical and pathologic features of the human HMSNs, but are interpreted in the context of basic research findings on the cellular and molecular biology of the peripheral nervous system derived from in vivo and in vitro studies in spontaneously-occurring and genetically engineered animal models for the HMSNs.

Expression of P0 protein in sural nerve of a patient with hereditary motor and sensory neuropathy type III

We present expression of Po protein and Po mRNA on the sural nerve of a patient with hereditary motor and sensory neuropathy type III. This patient was identified with a point mutation in Po gene, which resulted in the substitution of glycine for arginine in transmembrane domain of P0 protein. An electron microscopic examination revealed very thin myelinated fibers surrounded by multilamellated onion bulbs composed with greatly proliferated Schwann cells. An immunocytochemical and immunoblot analysis is showed P0 protein normally expressed in myelin on the sural nerve. By in situ hybridization, mRNA of P0 protein was detected at normal levels in Schwann cell cytoplasm. Those observations indicated that there was no truncated myelin P0 protein in peripheral nerve of this patient.

Hereditary motor and sensory neuropathy with myelin outfolding: clinical, genetic and neuropathological study of three cases

We describe 3 patients affected by a congenital motor and sensory neuropathy with excessive myelin outfoldings (MOs). Clinical and electrophysiological features supported the diagnosis of hereditary motor and sensory neuropathy (HMSN). The genetic study failed to demonstrate either the duplication in chromosome 17p11.2 or the mutations at exons 1 and 2 of the myelin protein gene, PMP-22, recently observed in HMSN type Ia, and suggested an autosomal recessive (AR) inheritance. Sural nerve biopsy revealed a demyelinating process with prominent hypertrophic changes and excessive MOs formation. The percentage of MOs was significantly higher than in 3 age-matched HMSN Ia patients. MOs were morphologically and morphometrically different from tomacular-like thickenings of myelin. Myelin thickness was significantly lower than in the three HMSN Ia controls and linear regression showed a thinner myelin related to axon diameter. The reported cases demonstrate that HMSN with MOs is a well defined variant of HMSN and that a primary defect in the myelination process may be proposed as a possible pathogenic mechanism.