Canavan Disease?

Canavan disease, one of the most common cerebral degenerative diseases of infancy, is a gene-linked, neurological birth disorder in which the white matter of the brain degenerates into spongy tissue riddled with microscopic fluid-filled spaces.

Canavan disease is one of a group of genetic disorders known as the leukodystrophies. These diseases cause imperfect growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fibers in the brain. Myelin, which lends its color to the "white matter" of the brain, is a complex substance made up of at least ten different chemicals. Each of the leukodystrophies affects one (and only one) of these substances. Canavan disease is caused by mutations in the gene for an enzyme called aspartoacylase.

Source: MedicineNet.com
http://www.medicinenet.com/canavan_disease/article.htm