A case report of congenital hypomyelination.

A 3 year, 11 month-old Japanese male with congenital hypomyelination is described. Clinical features are delay of motor development, generalized muscle hypotonia and weakness, absent tendon reflexes due to peripheral neuropathy, and normal mental development. Electrophysiologically, nerve conduction velocities could not be measured. Histological examination of the right sural nerve revealed total of absence myelin of most of the myelinated fibers. Electronmicroscopically, there was a concentric network of lamellae formed by double-layered sheets of basement membranes with fragments of Schwann cell cytoplasm around the myelinated fibers, so called "onion-bulbs". These peculiar features were similar to those in the cases reported by Lyon, (1969); Kennedy et al., (1977); Karch et al., (1975); and Anderson et al. (1973).