Galactocerebroside (GalCer or GalC) is the most frequently found glycosphingolipid in animals. GalCer consist of a ceramide linked to a single galactose residue at the 1-hydroxyl moiety. Cerebrosides are concentrated in nervous tissues where they increase from about 0.02% of the dry weight in human fetal brain to 2% in gray matter and 12% in white matter of adult brain. GalCer is a specific cell-surface antigenic marker for oligodendrocytes and schwann cells. GalCer is the largest single component of the myelin sheath of nerves. GalCer synthesis therefore serves as a measurement of myelin formation or remyelination. Krabbe disease is an autosomal recessive sphingolipidosis caused by deficient activity of the lysosomal hydrolase galactosylceramide beta-galactosidase (GALC). GALC mediates the degradation of GalCer and other terminal beta-Gal-containing sphingolipids, including psychosine (galactosylsphingosine). Increased psychosine levels are believed to lead to widespread destruction of oligodendroglia in the CNS and to subsequent demyelination.