HEXB and Sandhoff disease: β-hexosaminidase A is the deficient enzyme and is responsible for degrading GM2 into GM3 as a part of the ganglioside metabolism pathway.1,2 Three diseases are associated with GM2 gangliosidosis, Tay-Sachs disease is characterized by biallelic variants in HEXA encoding the α subunit of β-hexosaminidase A. Sandhoff disease is characterized by biallelic variants in HEXB encoding the ß subunit resulting in deficiencies in both hexosaminidase A and B. GM2 activator deficiency, known as the AB variant, is characterized by biallelic variants in GM2A.