Nerve and muscle biopsy in a case of hereditary motor and sensory neuropathy type III with basal lamina onion bulbs.

A girl presented at age 8 months with generalized hypotonia and areflexia. The parents were unrelated and without symptoms. At the age of 2 years and 10 months she was able to stand and walk with support. Intellectual development was normal. The mean fibre size in the lateral vastus muscle was normal, the variability was slightly increased. Type I and II fibres tended to be aggregated, but there was no type grouping. Motor and sensory nerve conduction velocities were less than 6 m/s. The sural nerve lacked myelin sheaths, and large non-myelinated axons were surrounded by concentric layers ('onion bulbs') of basal lamina material. The disease was classified as 'autosomal recessive hereditary motor and sensory neuropathy type III(HMSN (III) with basal lamina onion bulbs'. The muscle biopsy findings suggest that congenital amyelination or hypomyelination does not necessarily result in neurogenic atrophy.