A multicenter retrospective study of charcot-marie-tooth disease type 4B (CMT4B) associated with mutations in myotubularin-related proteins (MTMRs).

OBJECTIVE: Charcot-Marie-Tooth (CMT) disease 4B1 and 4B2 (CMT4B1/B2) are characterized by recessive inheritance, early onset, severe course, slowed nerve conduction, and myelin outfoldings. CMT4B3 shows a more heterogeneous phenotype. All are associated with myotubularin-related protein (MTMR) mutations. We conducted a multicenter, retrospective study to better characterize CMT4B. METHODS: We collected clinical and genetic data from CMT4B subjects in 18 centers using a predefined minimal data set including Medical Research Council (MRC) scores of nine muscle pairs and CMT Neuropathy Score. RESULTS: There were 50 patients, 21 of whom never reported before, carrying 44 mutations, of which 21 were novel and six representing novel disease associations of known rare variants. CMT4B1 patients had significantly more-severe disease than CMT4B2, with earlier onset, more-frequent motor milestones delay, wheelchair use, and respiratory involvement as well as worse MRC scores and motor CMT Examination Score components despite younger age at examination. Vocal cord involvement was common in both subtypes, whereas glaucoma occurred in CMT4B2 only. Nerve conduction velocities were similarly slowed in both subtypes. Regression analyses showed that disease severity is significantly associated with age in CMT4B1. Slopes are steeper for CMT4B1, indicating faster disease progression. Almost none of the mutations in the MTMR2 and MTMR13 genes, responsible for CMT4B1 and B2, respectively, influence the correlation between disease severity and age, in agreement with the hypothesis of a complete loss of function of MTMR2/13 proteins for such mutations. INTERPRETATION: This is the largest CMT4B series ever reported, demonstrating that CMT4B1 is significantly more severe than CMT4B2, and allowing an estimate of prognosis. ANN NEUROL 2019.

Are electrophysiological features related to disability in patients with anti-MAG neuropathy?

OBJECTIVES: To explore clinical-neurophysiological correlations in anti-myelin-associated glycoprotein (anti-MAG) neuropathy. METHODS: Clinical and electrophysiological data of 42 patients with anti-MAG neuropathy were retrospectively analysed. Disability was evaluated using the Overall Neuropathy Limitation Scale (ONLS), motor impairment through MRC sum score and sensory deficiency through INCAT sensory score. Compound motor action potential (CMAP) sum score was calculated adding the distal CMAP amplitude of the median, ulnar, tibial and fibular nerves of both sides. RESULTS: In multivariate analysis, motor impairment was associated with CMAP sum score (r=0.35, P=0.047) and distal motor latency in the median nerves (r=-0.45 P=0.012), sensory deficiency was related to motor conduction velocity in the median nerve (r=-0.65. P=0.02). Disability was correlated with CMAP sum score (r=-0.37, P=0.022). CONCLUSION: Electrophysiological features are associated with clinical involvement in anti-MAG neuropathy. Reduction of CMAP amplitudes reflects distal motor latency delay and is mainly due to axonal loss. Since it is related to muscle weakness and disability, CMAP sum score may be a good marker in the evaluation of patients with anti-MAG neuropathy.

[Dysferlinopathy. Example of a new myopathy]. / Dysferlinopathie. Exemple d'une nouvelle myopathie.

Over the past 10 years, the impact of modern microscopic pathology and molecular genetics on the knowledge of myopathies has been enormous. Dysferlinopathy is a good example. Dysferlin is a surface membrane protein without homology with known mammalian protein excepted otoferlin. It is encoded by a gene on chromosome 2. Miyoshi myopathy and limb girdle muscular dystrophy 2B have been reported to arise from defects in the same genetic locus (chromosome 2p 13). Some personal different examples are presented with typical features, high level of creatine kinase. Gene mutations, immunoblot and immunohistochemistry allow the diagnosis. Three clinical phenotypes are separated: distal myopathy, proximal myopathy, entire lower limbs posterior compartment amyotrophy. Structural changes are mild. Inflammation is not unusual and leads to the diagnosis of polymyositis. There are no correlation genotype-phenotype.