HEXA and Sandhoff disease: One of the main forms of GM2 gangliosidoses is Tay-Sachs disease associated with mutations in the HEXA gene, which encodes the α subunit of the lysosomal enzyme β-hexosaminidase A (HEXA), another form of GM2 gangliosidosis, known as Sandhoff disease, is specifically linked to mutations in the HEXB gene.