A new variant of Type-AB GM2-gangliosidosis

A patient diagnosed as having Type-AB GM2-gangliosidosis was found to have a defect in β-hexosaminidase A, but not in the activator (GM2-activator) specific for the enzymic hydrolysis of GM2 ganglioside. β-Hexosaminidase A and B isolated from the brain of the patient showed normal activity toward synthetic substrates, but could not hydrolyze GM2 ganglioside in the presence of GM2-activator isolated from normal human liver or brain. The level of GM2-activator in the brain of this patient was three times higher than that found in the two control brains. The activator isolated from the brain of this patient was able to stimulate the hydrolysis of GM2 ganglioside catalyzed by human hepatic or brain β-hexosaminidase A but not by B.