Intrafamilial variability in Machado-Joseph disease.

Dominantly inherited ataxias resulting from different gene mutations are difficult to distinguish based on clinical phenotypes. We believe the phenotypic variability within families can be a clue to clinical diagnosis. We illustrate the range of phenotypes extending from levodopa-responsive extrapyramidal disease to more purely ataxic syndromes seen in two families with molecularly proven Machado-Joseph disease.