Peripheral Myelin Protein 22 gene duplication with atypical presentations: A new example of the wide spectrum of Charcot-Marie-Tooth 1A disease

Current profile of Charcot-Marie-Tooth disease in Africa: A systematic review

BACKGROUND AND AIMS

Charcot-Marie-Tooth disease (CMT) is the most common inherited peripheral neuropathy characterised by a high clinical and genetic heterogeneity. While most cases were described in populations with Caucasian ancestry, genetic research on CMT in Africa is scant. Only a few cases of CMT have been reported, mainly from North Africa. The current study aimed to summarise available data on CMT in Africa, with emphasis on the epidemiological, clinical, and genetic features.

METHODS

We searched PubMed, Scopus, Web of Sciences, and the African Journal Online for articles published from the database inception until April 2021 using specific keywords. A total of 398 articles were screened, and 28 fulfilled our selection criteria.

RESULTS

A total of 107 families totalling 185 patients were reported. Most studies were reported from North Africa (n = 22). The demyelinating form of CMT was the commonest subtype, and the phenotype varied greatly between families, and one family (1%) of CMT associated with hearing impairment was reported. The inheritance pattern was autosomal recessive in 91.2% (n = 97/107) of families. CMT-associated variants were reported in 11 genes: LMNA, GDAP1, GJB1, MPZ, MTMR13, MTMR2, PRX, FGD4/FRABIN, PMP22, SH3TC2, and GARS. The most common genes reported are LMNA, GDAP1, and SH3TC2 and have been found mostly in Northern African populations.

INTERPRETATION

This study reveals that CMT is not rare in Africa, and describes the current clinical and genetic profile. The review emphasised the urgent need to invest in genetic research to inform counselling, prevention, and care for CMT in numerous settings on the continent.

Acute to Subacute Atraumatic Entrapment Neuropathies in Patients With CMT1A: A Report of a Distinct Phenotypic Variant of CMT1A

Charcot-Marie-Tooth type 1A (CMT1A) is typically characterised as a childhood-onset, symmetrical, length-dependent polyneuropathy with a gradual progressive clinical course. Acute to subacute neurological deterioration in CMT1A is rare, and has been reported secondary to overlap pathologies including inflammatory neuropathy. We identified two patients with CMT1A who presented with acute to subacute, atraumatic, entrapment neuropathies as an initial symptom. A superimposed inflammatory neuropathy was excluded. Both patients had a diffuse demyelinating polyneuropathy, with markedly low motor nerve conduction velocities (<20 m/s). In both patients, we demonstrated symptomatic and asymptomatic partial conduction blocks at multiple entrapment sites. Nerve ultrasound findings in our patients demonstrated marked diffuse nerve enlargement, more pronounced at non-entrapment sites compared to entrapment sites. We discuss ways to distinguish this condition from its other differentials. We propose pathophysiological mechanisms underlying this condition. We propose that CMT1A with acute to subacute, atraumatic, entrapment neuropathies to be a distinct phenotypic variant of CMT1A.

New evidence for secondary axonal degeneration in demyelinating neuropathies

Development of peripheral nervous system (PNS) myelin involves a coordinated series of events between growing axons and the Schwann cell (SC) progenitors that will eventually ensheath them. Myelin sheaths have evolved out of necessity to maintain rapid impulse propagation while accounting for body space constraints. However, myelinating SCs perform additional critical functions that are required to preserve axonal integrity including mitigating energy consumption by establishing the nodal architecture, regulating axon caliber by organizing axonal cytoskeleton networks, providing trophic and potentially metabolic support, possibly supplying genetic translation materials and protecting axons from toxic insults. The intermediate steps between the loss of these functions and the initiation of axon degeneration are unknown but the importance of these processes provides insightful clues. Prevalent demyelinating diseases of the PNS include the inherited neuropathies Charcot-Marie-Tooth Disease, Type 1 (CMT1) and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and the inflammatory diseases Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Secondary axon degeneration is a common feature of demyelinating neuropathies and this process is often correlated with clinical deficits and long-lasting disability in patients. There is abundant electrophysiological and histological evidence for secondary axon degeneration in patients and rodent models of PNS demyelinating diseases. Fully understanding the involvement of secondary axon degeneration in these diseases is essential for expanding our knowledge of disease pathogenesis and prognosis, which will be essential for developing novel therapeutic strategies.

Paternal gender specificity and mild phenotypes in Charcot-Marie-Tooth type 1A patients with de novo 17p12 rearrangements

Background

Charcot–Marie–Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP) are developed by duplication and deletion of the 17p12 (PMP22) region, respectively.

Methods

De novo rates were determined in 211 CMT1A or HNPP trio families, and then, analyzed gender‐specific genetic features and clinical phenotypes of the de novo cases.

Results

This study identified 40 de novo cases (19.0%). Paternal origin was highly frequent compared to maternal origin (p = .005). Most de novo CMT1A rearrangements occurred between non‐sister chromatids (p = .003), but it was interesting that three of the four sister chromatids exchange cases were observed in the less frequent maternal origin. Paternal ages at the affected child births were slightly higher in the de novo CMT1A group than in the non‐de novo CMT1A control group (p = .0004). For the disability score of CMTNS, the de novo CMT1A group had a slightly lower value compared to the control group (p = .005). Electrophysiological studies showed no significant differences between the two groups.

Conclusion

This study suggests that de novo CMT1A patients tend to have milder symptoms and that the paternal ages at child births in the de novo group are higher than those of the non‐de novo group.

PMP22 Gene-Associated Neuropathies: Phenotypic Spectrum in a Cohort from India

Reports of spectrum of clinical manifestations in PMP22 gene-associated neuropathies (duplication/mutations) are scarce. To identify the frequency of PMP22 gene variations and establish their genotype-phenotype correlation. Patients with suspected genetic demyelinating neuropathy (n = 128) underwent evaluation for copy number variations and point mutations in PMP22 gene by multiplex ligation-dependent probe amplification (MLPA) and direct sequencing respectively. Of these, only 27 patients (M:F:19:8) from 18 families had PMP22 gene-associated neuropathy; they were subsequently analyzed for genotype-phenotype correlation. Twenty-five patients had PMP22 duplication while two patients had PMP22 missense mutations (p.A114V and p.L80P). Age at onset of neuropathy ranged from infancy to 63 years and symptom duration ranged from 2 to 32 years. Cranial nerve dysfunction in the form of ptosis, ophthalmoplegia, bifacial weakness, and sensorineural hearing loss was observed in addition to a number of systemic features. Three patients were asymptomatic. All except one patient were ambulant. Velocity of median nerve and amplitude of evoked motor responses from common peroneal nerve were significantly reduced in male patients. There was significantly worse disability in the late-onset group as compared with the early-onset group. Otherwise, the mean age at onset, frequency of skeletal deformities, patterns of motor weakness, muscle stretch reflexes, sensory impairment, disability rating scales, and electrophysiological parameters were comparable irrespective of gender, onset age, family history and ulnar nerve conduction velocities. The relatively low frequency of PMP22 duplication in the present cohort warrants a more comprehensive search to establish the genetic etiology. Further research into the role of other genetic variants as well as modifier genes and their effect on phenotypic heterogeneity is indicated.

Hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is characterized by recurrent sensory and motor neuropathy in individual nerves starting in adolescence or young adulthood, focal conduction abnormalities at entrapment sites on nerve conduction studies, and sausage-like swellings (tomacula) of the myelin sheaths by nerve biopsy. It is characterized genetically by the deletion of the chromosome 17p11.2-p12 region including the peripheral myelin protein-22 gene in the overwhelming majority of cases. HNPP may be frequently underdiagnosed or misdiagnosed owing to the heterogeneity of clinical and electrophysiological appearance. The main objective of this review is to describe clinical manifestations, paraclinical features such as electrodiagnostic, pathological, radiological and genetics findings, and possible treatments.

Clinical and Pathological Variation of Charcot-Marie-Tooth 1A in a Large Chinese Cohort

Charcot-Marie-Tooth 1A (CMT1A) caused by peripheral myelin protein 22 (PMP22) gene duplication is the most common form of hereditary polyneuropathy. Twenty-four genetically confirmed CMT1A patients with sural nerve biopsies were enrolled in this study. The clinical picture included a great variability of phenotype with mean onset age of 22.2 ± 14.5 years (1-55 years). Pathologically, we observed a severe reduction in myelinated fiber density showing three types of changes: pure onion bulb formation in 3 cases (12.5%), onion bulb formation with axonal sprouts in 10 cases (41.7%), and focally thickened myelin with onion bulb formation or/and axonal sprouts in 11 cases (45.8%). We observed no significant correlation between nerve fiber density and disease duration. There was no significant difference between the 3 pathological types in terms of clinical manifestations, nerve fiber density, and g-ratio. Our study indicates that there is marked variability in the age of onset of CMT1A, as well as significant pathological changes without deterioration with the development of the disease. Focally thickened myelin is another common morphological feature of demyelination.

Re-emergence of hereditary polyneuropathy in Scandinavian Alaskan malamute dogs-old enemy or new entity? A case series

A homozygous mutation has been identified in the N-myc downstream-regulated gene 1 (NDRG1) in recent cases of polyneuropathy in Alaskan malamute dogs from the Nordic countries and USA. The objective of the present study was to determine if cases diagnosed 30-40 years ago with polyneuropathy in the Alaskan malamute breed in Norway had the same hereditary disease as the recent cases. Fourteen historical cases and 12 recently diagnosed Alaskan malamute dogs with hereditary polyneuropathy, and their parents and littermates (n = 88) were included in this study (total n = 114). After phenotyping of historical and recent cases, NDRG1 genotyping was performed using DNA extracted from archived material from five Norwegian dogs affected by the disease in the late 1970s and 1980s. In addition, pedigrees were analysed. Our study concluded that historical and recent phenotypic polyneuropathy cases were carrying the same NDRG1-mutation. The pedigree analysis showed that all affected Alaskan malamute cases with polyneuropathy could be traced back to one common ancestor of North American origin. By this study, a well-documented example of the silent transmission of recessive disease-causing alleles through many generations is provided, demonstrated by the re-emergence of a phenotypically and genetically uniform entity in the Scandinavian Alaskan malamute population.

Are electrophysiological criteria useful in distinguishing childhood demyelinating neuropathies?

Childhood chronic inflammatory demyelinating polyneuropathy (CIDP) needs to be differentiated from hereditary neuropathy. We aimed to validate existing CIDP nerve conduction study (NCS) criteria in a group of children with demyelinating neuropathies of chronic or subacute onset. Retrospective analysis of clinical and NCS results in 18 children with CIDP, 7 with hereditary neuropathy with pressure palsy (HNPP), and 24 with Charcot-Marie-Tooth 1a (CMT1a). AAN and EFNS electrodiagnostic CIDP criteria were fulfilled in 17 of 18 CIDP, 3 of 7 HNPP, and 23 of 24 CMT1a patients. A distal compound muscle action potential (dCMAP) of >9 ms was observed in 14 of 18 CIDP patients but not in any patients with HNPP. Abnormal median/normal sural SNAP (AMNS) and a 10 m/s difference between conduction velocities (CV) of two corresponding nerves were not observed in any CMT1a patients. NCS in CMT1a, HNPP, and CIDP reflect demyelination. dCMAP duration, sensory AMNS, and a 10 m/s CV difference parameter are most useful in the differential diagnosis of pediatric CIDP.

The genetics of Charcot-Marie-Tooth disease: current trends and future implications for diagnosis and management

Charcot–Marie–Tooth (CMT) disease is the most common hereditary polyneuropathy and is classically associated with an insidious onset of distal predominant motor and sensory loss, muscle wasting, and pes cavus. Other forms of hereditary neuropathy, including sensory predominant or motor predominant forms, are sometimes included in the general classification of CMT, but for the purpose of this review, we will focus primarily on the forms associated with both sensory and motor deficits. CMT has a great deal of genetic heterogeneity, leading to diagnostic considerations that are still rapidly evolving for this disorder. Clinical features, inheritance pattern, gene mutation frequencies, and electrodiagnostic features all are helpful in formulating targeted testing algorithms in practical clinical settings, but these still have shortcomings. Next-generation sequencing (NGS), combined with multigene testing panels, is increasing the sensitivity and efficiency of genetic testing and is quickly overtaking targeted testing strategies. Currently, multigene panel testing and NGS can be considered first-line in many circumstances, although obtaining initial targeted testing for the PMP22 duplication in CMT patients with demyelinating conduction velocities is still a reasonable strategy. As technology improves and cost continues to fall, targeted testing will be completely replaced by multigene NGS panels that can detect the full spectrum of CMT mutations. Nevertheless, clinical acumen is still necessary given the variants of uncertain significance encountered with NGS. Despite the current limitations, the genetic diagnosis of CMT is critical for accurate prognostication, genetic counseling, and in the future, specific targeted therapies. Although whole exome and whole genome sequencing strategies have the power to further elucidate the genetics of CMT, continued technological advances are needed.

Severe phenotypes in a Charcot-Marie-Tooth 1A patient with PMP22 triplication

Charcot-Marie-Tooth disease (CMT) is a genetically and clinically heterogeneous hereditary motor and sensory neuropathy signified by a distal symmetric polyneuropathy. The most frequent subtype is type 1A (CMT1A) caused by duplication in chromosome 17p12 that includes PMP22. This study reports a woman with a family history of CMT1A due to PMP22 duplication. However, she presented with a more severe phenotype than her sibling or ancestors and was found to have a PMP22 triplication instead of the duplication. This was caused by de novo mutation on her affected mother's duplication chromosome. Her lower limb magnetic resonance imaging revealed severe diffused atrophy and fatty replacement. However, her affected sister with typical PMP22 duplication showed almost intact lower limb. Triplication patient's median motor nerve conduction velocity was far lower compared with her sister. Her onset age was faster (8 years) than her sister (42 years). CMT1A triplication might be generated by a female-specific chromosomal rearrangement mechanism that is different from the frequent paternal-originated CMT1A duplication. It also suggests that the wide phenotypic variation of CMT1A might be partly caused by unstable genomic rearrangement, including PMP22 triplication.