Family history in juvenile Huntington disease: do the signs point to "yes" or "very doubtful"?

Juvenile Huntington disease (JHD)-Huntington disease (HD) with an onset ≤20 years-accounts for approximately 10% of all HD cases. Like the adult form of the disorder, JHD is a hereditary neurodegenerative disease characterized by dementia and behavioral changes, caused by an expanded CAG repeat within the first exon of the huntingtin (HTT) gene on chromosome 4.(1) Unlike the adult form, JHD tends to present with a rigid-dystonic picture or nonspecific motor and neuropsychological signs rather than chorea.(2,3.)