Background and Objectives: Distal hereditary motor neuropathy (dHMN) is a clinically and genetically heterogeneous group of inherited neuropathies. The objectives of this study were to report the clinical and genetic features of dHMN patients in a Chinese cohort.Aims and Methods: We performed clinical assessments and whole-exome sequencing in 24 dHMN families from Mainland China. We conducted a retrospective analysis of the data and investigated the frequency and clinical features of patients with a confirmed mutation.Results: Two novel heterozygous mutations in GARS, c.373G>C (p.E125Q) and c.1015G>A (p.G339R), were identified and corresponded to the typical dHMN-V phenotype. Together with families with WARS, SORD, SIGMAR1, and HSPB1 mutations, 29.2% of families (7/24) acquired a definite genetic diagnosis. One novel heterozygous variant of uncertain significance, c.1834G>A (p.G612S) in LRSAM1, was identified in a patient with mild dHMN phenotype.Conclusion: Our study expanded the mutation spectrum of GARS mutations and added evidence that GARS mutations are associated with both axonal Charcot-Marie-Tooth and dHMN phenotypes. Mutations in genes encoding aminoamide tRNA synthetase (ARS) might be a frequent cause of autosomal dominant-dHMN, and SORD mutation might account for a majority of autosomal recessive-dHMN cases. The relatively low genetic diagnosis yield indicated more causative dHMN genes need to be discovered.

Mutations in ganglioside-induced differentiation-associated-protein 1 (GDAP1) have been associated with both subtypes of Charcot-Marie-Tooth (CMT) disease, autosomal recessive (CMT4A and AR-CMT2K) and autosomal dominant (AD-CMT2K). Over 80 different mutations have been identified so far. With the use of Sanger sequencing and Next Generation Sequencing (NGS) technologies, we screened a cohort of 306 unrelated Chinese CMT patients and identified 8 variants in the GDAP1 gene in 4 families, 5 of which were novel (R41H, N201Kfs*5, Q38X, V215I and Q38R). Application of Bioinformatics tool and classification according to the American College of Medical Genetics (ACMG) predicted them of being likely pathogenic with the exception of one variant of uncertain significance (VUS). In addition, we detected the presence of a single heterozygous variant of uncertain significance H256R in one additional family from the CMT cohorts. We found a GDAP1 prevalence rate of 1.63% (5/306). Three families (families 1, 2 and 3) were found to have an autosomal recessive (AR) pattern of inheritance while family 4 displayed an autosomal dominant (AD) mode of inheritance. Electro-physiologic studies revealed an axonal type of neuropathy (AR-CMT2K and AD-CMT2K) in all affected individuals. Clinical characteristics and findings in our study demonstrated that the recessive form presented earlier in life and exhibited severe symptoms and rapid evolution compared to the dominant form. We observed a marked intra-familial variability within the AD family in terms of age at disease onset, symptom severity and clinical progression. Our study expands the mutational spectrum of GDAP1-related CMT disease with the identification of new and unreported GDAP1 variants and demonstrates the predominance of the axonal form of neuropathy in CMT disease associated with GDAP1. We highlight the clinical characteristics associated with these genotypes and describe the relative frequency of GDAP1 variants amongst the Chinese population.

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