HEXA and Sandhoff disease: Sandhoff disease occurs due to mutations in the HEXB (in human)/Hexb (in mouse) gene and the resulting deficiency of the β subunit of the enzyme hexosaminidase and the resulting excess central nervous system tissue accumulation of GM2, whereas Tay–Sachs disease occurs due to mutations in the HEXA (in human)/Hexa (in mouse) gene and the resulting deficiency of the α subunit of the hexosaminidase and the resulting excess central nervous system tissue accumulation of GM2 [24].