Juvenile progressive dystonia: a new phenotype of GM2 gangliosidosis.

A 10-year-old boy developed progressive dystonia and dementia. His symptoms had begun at age 2 1/2 years, and he had been unable to walk by 8 years. At age 10 he was severely dystonic, unable to use his hands to feed himself, and almost anarthric . He had dysphagia and urinary incontinence, and functioned at a 4-year-old level of mental development. The mean percentages of beta-hexosaminidase A measured in serum, leukocytes, and fibroblasts by the heat denaturation method, each on three separate assays, were 5.9, 9.8, and 13.0%, respectively. These values are higher than in Tay-Sachs disease but are similar to levels seen in late-onset or adult cases of GM2 gangliosidosis. This patient appears to represent a new phenotype of juvenile GM2 gangliosidosis having dystonia as the dominant symptom.