Delayed myelination in a patient with 18q- syndrome.

A Japanese boy with the typical manifestations of 18q-syndrome and delayed myelination on magnetic resonance imaging is described. Cytogenetic investigation revealed a deletion at 18q21.3. Three serial magnetic resonance images demonstrated that myelination in the central nervous system was delayed except for the corpus callosum and brainstem. This pattern of delayed myelination appears to be peculiar to the 18q- syndrome. Because the gene for myelin basic protein has been localized to the distal end of the long arm of chromosome 18, we speculate that the abnormal myelination in our patient was partly due to the failure of expression of the myelin basic protein gene.