Hexosaminidase A (alpha polypeptide),is an enzyme that is encoded by the HEXA gene.β-hexosaminidase occurs as two major isozymes: hexosaminidase A and hexosaminidase B. Hexosaminidase A and the cofactor GM₂ activator protein catalyze the degradation of the GM₂ gangliosides and other molecules containing terminal N-acetyl hexosamines. Hexosaminidase A is a heterodimer composed of an alpha and beta subunit. The alpha subunit is encoded by the HEXA gene while the beta subunit is encoded by the HEXB gene. Gene mutations in the gene encoding the beta subunit (HEXB) often result in Sandhoff disease; whereas, mutations in the gene encoding the alpha subunit (HEXA, this gene) decrease the hydrolysis of GM₂ gangliosides, which is the main cause of Tay-Sachs disease(GM2-gangliosidosis type I).