In the course of screening for heterozygotes for beta-hexosaminidase deficiency, the serum and white cells of a clinically normal father of deficient children were found to have an apparent deficiency for both hexosaminidases A and B, assayed with an artificial substrate, 4-methylumbelliferyl-beta-glucosaminide. No inhibitor was present. Assayed with a natural substrate, n-acetylgalactosaminyl beta 1-4 galactosyl beta 1-4 glucosyl ceramide, which had been isolated from the brain of a patient with Tay--Sachs disease and labeled in the terminal n-acetyl-galactosamine, a value in the heterozygote range was found. It was concluded that the proband is probably a double heterozygote for two mutations; one is the classic Sandhoff type (lack of hexosaminidases A and B), giving rise to deficient offspring when combined with the same mutation borne by the wife. The other obscures any activity with the artificial substrate but allows an action on natural substrates, explaining the normal life of its carrier.
