Late-onset hexosaminidase A and hexosaminidase A and B deficiency: family study and review.

Five children from two non-consanguineous Asian families with juvenile-onset hexosaminidase deficiency are presented. Two have juvenile Tay-Sachs disease with hexosaminidase A deficiency and three have juvenile Sandhoff disease with hexosaminidase A and B deficiency. The contributing factors in the spectrum of the hexosaminidase deficiency disease are outlined, and previously reported cases of late-onset Tay-Sachs and Sandhoff disease are reviewed. The heterogeneity of the effects of hexosaminidase deficiency is discussed, with the recommendation that the diagnosis be considered, in its various forms, when there is no other obvious explanation.