Clinical and genetic variations in the syndrome of adult GM₂ gangliodosis resulting from hexosaminidase a deficiency

Six patients from three families developed adult GM₂ gangliosidosis resulting from severe β‐hexosaminidase A deficiency. The clinical picture varied between and within families and included spinocerebellar, various motor neuron, and cerebellar connection syndromes. Psychosis appeared in each family. Involvement of three generations was recorded in one family. The phenotype of adult GM₂ gangliosidosis is variable and cannot form a basis for genetic classification. Detailed hexosaminidase determinations in eight patients from five families revealed all patients to have minor quantities of hexosaminidase A (about 15% of normal), with marked increase in hexosaminidase I isozyme.