Evolution of nerve conduction abnormalities in children with dominant hypertrophic neuropathy of the Charcot-Marie-Tooth type.

Serial motor conduction velocities and distal motor latencies were determined in two pairs of dizygotic twins, each born to a parent with dominant hypertrophic neuropathy of the Charcot-Marie-Tooth type (HMSN-I). Motor nerve conduction velocities could not distinguish between the normal and affected twin of the first pair studied at birth. Distal motor latency in the affected twin at birth, however, was borderline prolonged. The affected twin of the second pair had slowed motor velocities at age 17 months, but the extent of conduction slowing had not yet fully developed. Studies of these patients and the affected family members showed that maximal slowing of motor nerve conduction velocities evolved over the first 3-5 years of life in HMSN-I. Prolongation of distal motor latency may be the earliest abnormality observed in HMSN-I and this abnormality evolves over 10 or more years.