A follow-up study of isolated cases of suspected Huntington's disease.

We reviewed 49 patients in whom a diagnosis of Huntington's disease (HD) seemed possible on clinical grounds, but who gave no history of definitely affected relatives. In 32 with the typical clinical features of HD (progressive chorea and dementia, postural instability, abnormal initiation of saccadic eye movements), the diagnosis was confirmed in 7 patients who had had autopsies, affected relatives were found in 5 others, and HD remained probable in a further 13 who were reexamined. In the 17 with a less typical clinical picture, a diagnosis of HD appeared most likely in 2; other causes for chorea such as cerebrovascular disease, neuroacanthocytosis, recrudescence of Sydenham's chorea, and drug-induced tardive dyskinesia could be invoked in the remainder. We conclude that the likelihood of HD in a patient with the typical clinical features of this disorder but no history of affected relatives is at least 75%, which for practical purposes implies a risk to their children hardly less than in familial HD. The most plausible explanations for seemingly sporadic patients with HD are nonpaternity and mild, late-onset disease that is overlooked by other family members.