Infantile globoid cell leukodystrophy (GLD, or Krabbe disease) is a rare, inherited degenerative disorder of the central and peripheral nervous systems. It is characterized by the presence of globoid cells (multinucleated cells), the breakdown of the nerve's protective myelin coating, and destruction of brain cells. Globoid cell leukodystrophy is one of a group of genetic disorders called the leukodystrophies. These disorders impair the growth or development of the myelin sheath, and causes severe degeneration of mental and motor skills. Myelin, which lends its color to the "white matter" of the brain, is a complex substance made up of a number of different glucoproteins and glucolipids, the most important of which is galactocerebroside. Each of the leukodystrophies affects one of these substances. Globoid cell leukodystrophy is caused by a deficiency of galactocerebroside ß-galactosidase (GALC), an essential enzyme for myelin metabolism. The disease most often affects infants, with onset before the age of 6 months, but can occur in adolescence or adulthood. Symptoms include irritability, unexplained fever, limb stiffness (hypertonia), seizures, feeding difficulties, vomiting, and slowing of mental and motor development. Other symptoms include muscle weakness, spasticity, deafness, and blindness.