Distal hereditary motor neuropathy type II (distal HMN II): mapping of a locus to chromosome 12q24.

The distal hereditary motor neuropathy (distal HMN) or the spinal form of Charcot-Marie-Tooth (CMT) disease is an exclusively motor disorder of the peripheral nervous system. The disorder clinically resembles the hereditary motor and sensory neuropathies (HMSN) type I and type II or CMT type 1 and type 2. Distal HMN might also be related to the spinal muscular atrophies (SMA) since, in both disorders, the lower motor neurons are affected. Electrophysiological and neuropathological examinations of peripheral nerves show the absence of sensory involvement. We performed a genome search in an extended Belgian family with autosomal dominant distal HMN type II. Significant linkage was obtained with markers located at chromosome 12q24, and the gene for distal HMN II was assigned to the 13 cM interval between D12S86 and D12S340.

Linkage and mutation analysis of Charcot-Marie-Tooth neuropathy type 2 families with chromosomes 1p35-p36 and Xq13.

A locus for autosomal dominant Charcot-Marie-Tooth disease type 2 (CMT2A) was assigned by linkage analysis to chromosome 1p35-p36. We examined 11 unrelated CMT2 families for linkage to CMT2A using short tandem repeat (STR) polymorphisms. Only one family showed suggestive evidence for linkage to 1p35-p36. Further, because of an overlap in electrophysiologic data between CMT2 and CMTX female patients, we screened 6 of 11 CMT2 families compatible with dominant X-linkage for mutations in the connexin 32 (Cx32) gene at Xq13. There was a Cx32 mutation in one family, whereas another family showed suggestive evidence for Xq13 linkage upon analysis with STR polymorphisms. Our results suggest that the CMT2A locus is a minor locus for CMT2, additional linkage studies are needed to localize other CMT2 loci, and Cx32 mutations may be the underlying genetic defect in some CMT2 families.