The clinical features of hereditary motor and sensory neuropathy types I and II.

Observations have been made on a series of 228 patients with hereditary motor and sensory neuropathy, comprising 120 index cases and 108 affected relatives. These could be separated into genetically distinct type I and type II categories depending upon whether motor nerve conduction velocity in the median nerve was below or above 38 m s-1. These disorders constitute separate genetic subgroups within the clinical spectrum of 'peroneal muscular atrophy'. Type I cases were more numerous. Most were of autosomal dominant inheritance, but a proportion were sporadic. Four families with probable autosomal recessive inheritance were identified; these displayed significantly slower motor conduction velocity. There was a positive correlation between motor conduction velocity in the propositi and that in their relatives in the total type I group which persisted after the autosomal recessive cases had been extracted, indicating further genetic heterogeneity amongst the autosomal dominant families. No X-linked recessive families were encountered. Type I cases had a peak age of onset of symptoms during the first decade of life. In comparison with the type II cases, they displayed a greater tendency to show weakness of the hands, upper limb tremor and ataxia, generalized tendon areflexia and more extensive distal sensory loss, sometimes with acrodystrophic changes. Foot and spinal deformities were more frequent, probably due to the earlier age of onset. Nerve thickening was confined to the type I cases. The onset of symptoms was most often in the second decade in the type II cases, but in some it was delayed, even as late as the seventh decade. Most cases were again of autosomal dominant inheritance, but two probable autosomal recessive families were detected, as well as sporadic cases. Upper limb tremor also occurred in this form but was considerably less common. In both types, males tended to be more severely affected, and asymptomatic affected family members ('formes frustes') were more commonly female.