Juvenile progressive dystonia: A new phenotype of G M2 Gangliosidosis

A 10‐year‐old boy developed progressive dystonia and dementia. His symptoms had begun at age 2½ 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 β‐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 G M2 gangliosidosis. This patient appears to represent a new phenotype of juvenile G M2 gangliosidosis having dystonia as the dominant symptom.