Tay-Sachs disease: B1 variant.

This first child of non-Jewish parents had nystagmus at 4 months of age, bilateral cherry-red macular spots at 7 months of age, and hyperacusis at 8 months of age; the patient has deteriorated progressively following a clinical course typical of Tay-Sachs disease B variant. Total beta-N-acetylhexosaminidase assayed with 4-methylumbelliferyl-beta-glucosamine (4 MU GlcNAc) as substrate was within the normal range in plasma and cultured dermal fibroblasts and 2/3 the normal mean in leukocytes. The hexosaminidase A activity, assayed with the same substrate in plasma and cultured fibroblasts, approximated Tay-Sachs disease heterozygote levels; however, the activity of hexosaminidase A assayed with 4 MU Glc NAc-6-sulfate in the plasma, leukocytes, and cultured fibroblasts was less than 8, 2, and 1%, respectively of the control mean. This female infant with the B1 variant of Tay-Sachs disease demonstrated an earlier onset and more rapidly progressive course than was observed in 4 of the 5 previously reported patients with this Tay-Sachs disease variant.