Hereditary motor and sensory neuropathy with deafness, mental retardation, and absence of sensory large myelinated fibers: confirmation of a new entity.

We describe two brothers, 11 and 13 years old, respectively, with an early-onset hereditary motor and sensory neuropathy, deafness, and mental retardation. Electrophysiological studies showed marked reduction of motor and sensory conduction velocity and absence of sensory action potentials. Sural nerve biopsy, performed in both patients, showed absence of large myelinated fibers with normal density of small myelinated fibers without axonal degeneration. Signs of demyelination were found only in the younger patient. We suggest that motorsensory neuropathy associated with deafness and mental retardation with absence of large myelinated fibers on sural nerve biopsy represents a distinct clinicopathological entity, which is transmitted in families probably as an autosomal recessive trait.