Biochemical Basis of Type AB GM2 Gangliosidosis in a Japanese Spaniel

: The biochemical basis of a case of GM2 gangliosidosis in a Japanese Spaniel was studied. This dog had a massive accumulation of GM2 ganglioside in the brain. The β‐hexosaminidase activity in this affected dog brain was ∼ 12 times higher than that of normal brain. However, the activity toward p‐nitrophenyl‐6‐sulfo‐2‐acetamido‐2‐de‐oxyglucopyranoside was only four times higher in the affected brain than in normal brain. The GM2 activator preparation obtained from the normal dog brain could stimulate the hydrolysis of GM2 ganglioside by β‐hexosaminidase isolated from the affected dog. However, the corresponding activator fraction from the affected dog could not stimulate such a reaction. It was concluded that the biochemical basis of the Gm2 gangliosidosis in this Japanese Spaniel was due to the attenuation in the stimulatory activity of GM2 activator. This case represents the first animal form similar to the activator deficiency (or defect) of Type AB GM2 gangliosidosis in humans.