Juvenile Huntington disease.

Huntington disease (HD) is a dominantly inherited neurodegenerative disorder related to expansion of a triplet repeat sequence in the huntington gene on chromosome 4. Adult HD usually presents with chorea and personality changes. Juvenile HD is far less common and presents with parkinsonism, dystonia and seizures. We report a case of juvenile HD, showing extreme anticipation, in which diagnosis was delayed because of failure to recognise the significance of the family history and the characteristic clinical and radiologic features of this condition.