The juvenile and chronic forms of GM2 gangliosidosis: clinical and enzymatic heterogeneity.

We report the cases of 5 patients from 2 sibships with the "adult" or chronic form of GM2 gangliosidosis and 2 patients from another sibship with the juvenile form. We demonstrated hexosaminidase A deficiency in all cases but in 1 sibship the enzymatic profile was identical to that in Tay-Sachs disease, whereas in the remaining 2 families it was that of the B1 variant. There was no correlation between the clinical features and the enzymatic profile. Hexosaminidase A deficiency should be considered in unexplained progressive neurologic disorders of childhood and adolescence, including isolated dementia. EMG evidence of anterior horn cell involvement in association with neurologic or cognitive deterioration may be a diagnostic clue in the juvenile forms.