Huntington's disease in monozygotic twins reared apart.
Monozygotic twins, identical by serological studies, with Huntington's disease are described who were raised in separate households from birth. Age at onset, landmarks of the disease, and behavioural abnormalities were strikingly similar. Previously reported twin studies in Huntington's disease are reviewed. Twin data support the hypothesis that age at onset and several other clinical features of the illness are substantially determined by genetic mechanisms.