Inheritance of the enzyme defect in a new hexosaminidase deficiency disease

A new form of hexosaminidase deficiency disease is characterized clinically by mild, juvenile-onset, very slowly progressive cerebellar ataxia with macular cherry-red spots and absence of other findings. Biochemically there is striking hexosaminidase deficiency in serum, leukocytes, and fibroblasts. Hexosaminidase B appears absent, but hexosaminidase A–like and S–like activity is present on strach-gel electrophoresis. We studied hexosaminidase in leukocytes and serum from members of an affected patient's family and traced the enzyme defect through four generations. Leukocyte heat-stabile hexosaminidase in obligate and presumptive carriers was depressed both in specific activity (nanomoles per milligram of protein per hour) and as a percentage of total hexosaminidase. The carrier state was expressed in serum, but overlap with controls made this test unreliable. The similarity of these carriers to carriers of Sandhoff disease suggests that the disorders may be closely related, perhaps as allelic mutations of the hexosaminidase β subunit. Those involved with screening for Tay-Sachs disease should be aware that persons with an increased percentage of hexosaminidase A—that is, a decreased heat-stabile fraction—may be carriers of hexosaminidase deficiency diseases.