Apparent hexosaminidase B deficiency in two healthy members of a pedigree

A family is described in which all members have decreased serum and leukocyte hexosaminidase activity. Two individuals, the mother and the younger daughter, have a normal ratio of hexosaminidase B (HEX B) to total hexosaminidase, but their serum enzymes display respectively partial or complete lability to heat. It is proposed that the proband is a double heterozygote for the Sandhoff allele and for an allele producing thermolabile beta subunits.