METACHROMATIC LEUKODYSTROPHY

rare inherited metabolic disease in which the lack of a key enzyme causes loss of the protective myelin sheath from the white matter of the brain, resulting in psychological disturbances, mental deterioration, and sensory and motor defects. The absence of the enzyme cerebroside sulfatase (arylsulfatase A) allows certain specialized lipids (sphingolipids) to accumulate in nerve tissues instead of being broken down. At least two types of the disorder, infantile and adult, have been identified; a third, intermediate juvenile variety is sometimes recognized as well. In the more common infantile disease, the child develops normally for up to two years; the progressive onset of behavioral problems, mental deterioration, and blindness ends, after several years, in death. The adult disease is characterized mainly by psychological disturbances, including dementia. The juvenile form resembles infantile disease but is distinguished by later onset and a more protracted course.