HEXB and GM2 gangliosidosis: 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 [3].