The phenotype of Charcot-Marie-Tooth disease type 4C due to SH3TC2 mutations and possible predisposition to an inflammatory neuropathy

Abstract

Charcot-Marie-Tooth (CMT) disease is a heterogeneous group of inherited peripheral motor and sensory neuropathies. The locus responsible for CMT4C was previously assigned to the chromosome 5q23 region by homozygosity mapping and mutations in the SH3TC2 (KIAA1985) gene have been subsequently identified mainly in families around the Mediterranean basin but also frequently in European Gypsies. No English families have been reported to date. To determine the frequency, phenotype and neuropathology of CMT due to SH3TC2 mutations we screened 23 English autosomal recessive (AR) demyelinating CMT families. Five families with AR demyelinating CMT and SH3TC2 mutations were identified, four families were homozygous for the R954X mutation and the fifth family was compound heterozygous for the R954X and E657K mutations. There was significant clinical variation between these families with some cases presenting with a severe childhood onset neuropathy with respiratory and cranial nerve involvement, compared to other families with mild scoliosis and foot deformity. Characteristic sural nerve neuropathology was seen in three families with frequent demyelinating fibres surrounded by excess Schwann cell lamellae forming basal lamina onion bulbs and abnormally long and attenuated Schwann cell processes. One patient homozygous for the R954X mutation had a 20-year history of an inflammatory neuropathy that was superimposed onto the hereditary form, indicating that structural alterations to the SH3TC2 gene could possibly predispose to peripheral nerve inflammation.