Observations have been made on the peripheral nerve changes in four patients, 
ranging in age from 4 to 32 years, with the congenital cataracts facial 
dysmorphism neuropathy syndrome. Myelinated fibre density was within normal 
limits. The salient abnormality was diffuse hypomyelination which, in the older 
patients, was associated with demyelination and then axonal degeneration. These 
findings could be correlated with the relative preservation of sensory action 
potential amplitude despite markedly reduced nerve conduction velocity. 
Unmyelinated axon density was preserved. The morphological observations suggest 
the operation of a developmental process affecting myelination with a later 
superimposed degenerative disorder.