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Similar hereditary motor neuropathies are not allelic disorders

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A study in two families has suggested that different forms of peroneal muscular atrophy with vocal chord paralysis are caused by a separate gene or genes and not by an allele of the gene predisposing to one form—distal hereditary motor neuropathy type VII (dHMN-VII).

Both families had a phenotypically similar condition to dHMN-VII. The occurrence of disease among affected and unaffected family members, however, did not fit with the pattern of inheritance of the DHMNVP gene, which is responsible for dHMN-VII and maps to chromosome 2q14.

In one family with hereditary motor and sensory neuropathy type II (HMSN-IIC) one affected twin and one unaffected twin had the same haplotype of chromosome 2q14 from their affected mother. Two point LOD scores between the disease and markers of the DHMNVP gene were all negative. In the other family, with vocal cord paralysis and sensorineural deafness and distal muscle atrophy, two affected siblings had inherited opposite haplotypes of chromosome 2q14 from their affected mother. Again, LOD scores were all negative.

The two selected families had neurological and electrophysiological examinations, and their DNA was tested for linkage to the DHMNVP gene with 10 microsatellite markers spanning the gene. The researchers had already shown that the DHMNVP gene on chromosome 2q14 predisposed to dHMN-VII and sought to test the suggestion by others that this condition and HMSN-IIC might be allelic disorders.