A ganglioside storage disorder caused by a deficiency of enzymes B and C isoenzymes of beta-galactosidase with resulting accumulation of ganglioside MM1 in the brain and large amounts of keratosulfate-like mucopolysaccharide in the visceral organs. The affected infants appear normal at birth . Locomotor ataxia, the initial symptoms with onset at about one year of life, is followed by strabismus, inability to control hand movements, slurred speech, muscle weakness of the extremities, rapidly progressive psychomotor deterioration, dullness of senses, lethargy, seizures, decerebrate rigidity, and terminal bronchopneumonia at the age of 3 to 10 years and rarely later.