Hereditary heat-labile hexosaminidase B: A variant whose homozygotes synthesize a functional HEX A

Homozygosity for a mutant allele at the β-chain locus of hexosaminidase (HEX), resulting in a variant of heat-labile HEX B, is reported for the first time in two healthy children. HEX activity in their sera, leukocytes, and cultured skin fibroblasts is severely deficient when measured on the synthetic substrate 4-MU-GLcNAc. However, their cultured skin fibroblasts synthesize and process both α and β chains of HEX, and their lymphoid cells hydrolyze normally the natural ganglioside G(M2). This mutation is, therefore, different from at least one of the β-chain mutations found in previously published families with heat-labile HEX B.