form of gangliosidosis characterized by accumulation of G(M1) ganglioside and oligosaccharides in lysosomes caused by an absence or severe deficiency of the enzyme beta-galactosidase (type A1); three phenotypes of this disorder are infantile (generalized), juvenile, and adult; the infantile form is characterized by skeletal abnormalities, hypotonia, poor psychomotor development, hirsutism, hepatosplenomegaly, and facial abnormalities; the juvenile form features hyperacusis, seizures, and psychomotor retardation; the adult form features progressive intellectual deterioration, involuntary movements, ataxia, and spasticity.