Longitudinal Clinical and Biological Characteristics in Juvenile-Onset Huntington's Disease.

Background: Juvenile-onset Huntington's disease (JOHD) is a rare form of Huntington's disease (HD) characterized by symptom onset before the age of 21 years. Observational data in this cohort is lacking.

Objectives: Quantify measures of disease progression for use in clinical trials of patients with JOHD.