The significance of "unspecific neuropathy" in hereditary ataxias and related disorders

Neurological findings such as polyneuropathy, hyporeflexia, deformities, ataxic signs, and inverted plantar responses were found more frequently in unaffected sibs and other close relatives of people with hereditary ataxias or allied disorders (HA) than in a normal population sample. Introduction of a scoring system for neurological signs allowed the degree of neurological impairment to be estimated. The number of people with scores exceeding the limit of normality (sum score higher than 3.4) was counted among the members of HA families. This number was found to be greater in families where HA segregated as a recessive trait than those where it segregated as an autosomal dominant trait. The frequency of cases with high scores ("unspecific neuropathy" (Un)) observed in 1st and 2nd degree relatives of patients with dominant HA, suggested a hereditary basis for Un. The ratios were not compatible with simple Mendelism, but the observations fitted well with a hypothesis of polygenic inheritance. Un clustering in families with autosomal dominant HA could be due to a selection phenomenon through a negative assortative mating. Un cases observed in families with recessive HA may, in several instances, reflect disease manifestations in heterozygotes.