Hereditary motor and sensory neuropathy type II. Clinicopathological study of a family.

A family with hereditary motor and sensory neuropathy (HMSN) type II is described in which 10 affected and 17 unaffected members in three generations were examined. The peak age of onset was in the second decade. In the youngest generation, the proportion of affected to unaffected individuals at risk significantly differed from the expected 50%. There was slight slowing of conduction velocities in 36% of nerves; however, only 3 out of 10 affected members had entirely normal conduction studies. The amplitude of the sensory potentials of median and peroneal nerves was almost uniformly reduced. In all affected patients electromyography of anterior tibial muscles showed signs of neurogenic involvement. Histological study of two sural nerves and a sciatic nerve and its branches revealed loss of myelinated fibres with a proximal-to-distal gradient in this fibre loss, clusters of small regenerating fibres, and atrophic axons. Postmortem study of the proband showed loss of anterior horn and dorsal root ganglion neurons in the lumbar and sacral segments and degeneration of the fasciculus gracilis. Morphometric evaluation of L5 ventral and dorsal roots revealed a normal number of myelinated fibres, diameter histograms being shifted to the left because of a significant loss of large myelinated fibres and regeneration. These anatomical findings are consistent with the hypothesis that HMSN type II represents a primary neuronopathy affecting motor and sensory neurons.