The study aims to monitor the progression of symptoms and signs of those affected by JHD using modified UHDRS scales of motor and function (functional assessment, TFC). This will provide some basic data to analyse the usefulness of the proposed rating scales. Specifically, the initial aim is to assess these rating scales using an iterative process.

There may be significant delays in diagnosis of JHD especially if the young person presents with behavioural problems. Caregivers will be asked questions to capture the number of contacts with professionals in the time between onset of concerns about the young person and the confirmation of diagnosis.

Aim is to monitor the progression of symptoms and signs of those affected by JHD using modified UHDRS scales of motor and function (functional assessment, TFC). This will provide some basic data to analyse the usefulness of the proposed rating scales.

Juvenile Huntington's disease (JHD), defined as motor symptom onset before 21 years of age, has been recognised as being at one end of the phenotypic spectrum of HD. In many studies the proportion of cases meeting this definition has varied, but it is usually less than 10% and more probably 5%.

At present, no treatment is available which will alter the natural history of the condition; however, there is considerable research activity being undertaken to identify novel treatments. Any new disease-modifying treatment will have to be evaluated in a clinical trial with a predetermined outcome measure. Given the relatively slow rate of progression of HD, such a trial may have to last several years and as a consequence be less attractive from a commercial perspective. Patients with JHD have more extensive pathology but are frequently excluded from clinical trials because of the differing phenotype; this study will assess the feasibility of using this rating scale; if it or a further modification can be used and is sensitive to disease progression over relatively short time periods, then it is likely to have a significant impact on study trial design and cost.

Given the rarity of JHD, wide collaboration of scientists, clinicians and families affected by JHD internationally is important. As might be expected, the pathology in JHD is more widespread. Therefore, we need the ability to assess treatments, which alter the natural history on this subgroup of patients.

Inclusion Criteria:

• A clinical diagnosis of Juvenile-onset HD (motor onset as measured by TMS > 5, Diagnostic Confidence level = 4, AND age of onset aged 25 or younger).
• With family history of HD or DNA testing results demonstrating the presence of the HD mutation (i.e. a CAG repeat expansion within the HD gene >35 on larger allele).
• All participants must be able to provide consent for themselves, have a parent/guardian who can provide parental permission, or have an authorized legal representative who can provide consent.

Exclusion Criteria:

• Participants who are unable to understand the study protocol or unable to give informed consent, and have no legal representative.
• Age of onset ≥26

HD patients of all ages with an age of onset below 26