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Although mutations in more than 90 genes are known to cause CMT, the underlying genetic cause of CMT remains unknown in more than 50% of affected individuals. The discovery of additional genes that harbor CMT2-causing mutations increasingly depends on sharing sequence data on a global level. In this way-by combining data from seven countries on four continents-we were able to define mutations in ATP1A1, which encodes the alpha1 subunit of the Na + ,K + -ATPase, as a cause of autosomal-dominant CMT2. Seven missense changes were identified that segregated within individual pedigrees: c.143T>G (p.Leu48Arg), c.1775T>C (p.Ile592Thr), c.1789G>A (p.Ala597Thr), c.1801_1802delinsTT (p.Asp601Phe), c.1798C>G (p.Pro600Ala), c.1798C>A (p.Pro600Thr), and c.2432A>C (p.Asp811Ala). Immunostaining peripheral nerve axons localized ATP1A1 to the axolemma of myelinated sensory and motor axons and to Schmidt-Lanterman incisures of myelin sheaths. Two-electrode voltage clamp measurements on Xenopus oocytes demonstrated significant reduction in Na + current activity in some, but not all, ouabain-insensitive ATP1A1 mutants, suggesting a loss-of-function defect of the Na + ,K + pump. Five mutants fall into a remarkably narrow motif within the helical linker region that couples the nucleotide-binding and phosphorylation domains. These findings identify a CMT pathway and a potential target for therapy development in degenerative diseases of peripheral nerve axons., (Copyright © 2018 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Mutations in VCP have been reported to account for a spectrum of phenotypes that include inclusion body myopathy with Paget's disease of the bone and frontotemporal dementia, hereditary spastic paraplegia, and 1-2% of familial amyotrophic lateral sclerosis. We identified a novel VCP mutation (p.Glu185Lys) segregating in an autosomal dominant Charcot-Marie-Tooth disease type 2 family. Functional studies showed that the Glu185Lys variant impaired autophagic function leading to the accumulation of immature autophagosomes. VCP mutations should thus be considered for genetically undefined Charcot-Marie-Tooth disease type 2., (© The Author (2014). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Charcot Marie Tooth disease (CMT) affects one in 2500 people. Genetic testing is often pursued for family planning purposes, natural history studies and for entry into clinical trials. However, identifying the genetic cause of CMT can be expensive and confusing to patients and physicians due to locus heterogeneity., Methods: We analyzed data from more than 1000 of our patients to identify distinguishing features in various subtypes of CMT. Data from clinical phenotypes, neurophysiology, family history, and prevalence was combined to create algorithms that can be used to direct genetic testing for patients with CMT., Findings: The largest group of patients in our clinic have slow motor nerve conduction velocities (MNCV) in the upper extremities. Approximately 88% of patients in this group have CMT1A. Those who had intermediate MNCV had primarily CMT1X (52.8%) or CMT1B (27.8%). Patients with very slow MNCV and delayed walking were very likely to have CMT1A (68%) or CMT1B (32%). No patients with CMT1B and very slow MNCV walked before 15 months of age. Patients with CMT2A form our largest group of patients with axonal forms of CMT., Interpretation: Combining features of the phenotypic and physiology groups allowed us to identify patients who were highly likely to have specific subtypes of CMT. Based on these results, we created a series of algorithms to guide testing. A more detailed review of this data is published in Annals of Neurology (1).

Distal hereditary motor neuropathies comprise a clinically and genetically heterogeneous group of disorders. We recently mapped an X-linked form of this condition to chromosome Xq13.1-q21 in two large unrelated families. The region of genetic linkage included ATP7A, which encodes a copper-transporting P-type ATPase mutated in patients with Menkes disease, a severe infantile-onset neurodegenerative condition. We identified two unique ATP7A missense mutations (p.P1386S and p.T994I) in males with distal motor neuropathy in two families. These molecular alterations impact highly conserved amino acids in the carboxyl half of ATP7A and do not directly involve the copper transporter's known critical functional domains. Studies of p.P1386S revealed normal ATP7A mRNA and protein levels, a defect in ATP7A trafficking, and partial rescue of a S. cerevisiae copper transport knockout. Although ATP7A mutations are typically associated with severe Menkes disease or its milder allelic variant, occipital horn syndrome, we demonstrate here that certain missense mutations at this locus can cause a syndrome restricted to progressive distal motor neuropathy without overt signs of systemic copper deficiency. This previously unrecognized genotype-phenotype correlation suggests an important role of the ATP7A copper transporter in motor-neuron maintenance and function., (Copyright 2010 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Charcot-Marie-Tooth disease type 1A (CMT1A) is caused by a 1.4 Mb duplication on chromosome 17p11.2, which contains the peripheral myelin protein-22 (PMP22) gene. Increased levels of PMP22 in compact myelin of peripheral nerves have been demonstrated and presumed to cause the phenotype of CMT1A. The objective of the present study was to determine whether an extra copy of the PMP22 gene in CMT1A disrupts the normally coordinated expression of PMP22 protein in peripheral nerve myelin and to evaluate PMP22 over-expression in patients with CMT1A and determine whether levels of PMP22 are molecular markers of disease severity. PMP22 expression was measured by taking skin biopsies from patients with CMT1A (n = 20) and both healthy controls (n = 7) and patients with Hereditary Neuropathy with liability to Pressure Palsies (HNPP) (n = 6), in which patients have only a single copy of PMP22. Immunological electron microscopy was performed on the skin biopsies to quantify PMP22 expression in compact myelin. Similar biopsies were analysed by real time PCR to measure PMP22 mRNA levels. Results were also correlated with impairment in CMT1A, as measured by the validated CMT Neuropathy Score. Most, but not all patients with CMT1A, had elevated PMP22 levels in myelin compared with the controls. The levels of PMP22 in CMT1A were highly variable, but not in HNPP or the controls. However, there was no correlation between neurological disabilities and the level of over-expression of PMP22 protein or mRNA in patients with CMT1A. The extra copy of PMP22 in CMT1A results in disruption of the tightly regulated expression of PMP22. Thus, variability of PMP22 levels, rather than absolute level of PMP22, may play an important role in the pathogenesis of CMT1A.