Congenital hypomyelination neuropathy with arthrogryposis multiplex congenita.

A term male infant is described with an isolated disorder of peripheral myelination. At necropsy, the great majority of medium-to-large axons were unmyelinated. Electron microscopy showed normal axons and redundant lamination of basement membrane, suggestive of early onion bulb pathology. Immunohistochemistry of peripheral nerve showed deficiency of the myelin proteins P2 and P0, myelin basic protein, and myelin-associated glycoprotein. Arrest of peripheral myelination at the promyelin stage appears to be the origin of myelin deficiency.