The AB-variant of GM2-gangliosidosis. Clinical, biochemical, and pathological studies of two patients.

Clinical, neuropathological, and biochemical studies are reported in two children with the AB-variant of GM2-gangliosidosis. One patient had become symptomatic by 1--1.5 years, initially showing cerebellar signs, and then progressive psychomotor retardation, with hypotonia, spasticity, dementia, and macular cherry red spots, until death at the age of 4.5 years. The second patient showed an earlier onset of retardation and a more rapidly progressive course. At postmortem, the brains were of normal or near normal weights and displayed grossly only mild cerebral cortical and cerebellar atrophy, and mild pallor or attenuation of the white matter. Neuronal storage was widespread throughout the CNS, and both neurons and glia contained a variety of abnormal, membranous inclusions. Visceral organs were not involved. Ganglioside sialic acid was increased several fold in gray matter, with GM2 the predominant ganglioside species. N-acetyl-beta-glucosaminidase activities in serum, leukocytes, fibroblasts, and postmortem gray matter, assayed with an artificial, fluorogenic substrate, were normal, as were activities of other lysosomal hydrolases.