This is a multi-centre, multi-national, prospective, observational study of Huntington's disease (HD) with a control group of volunteers to:

• obtain natural history data on many HD mutation carriers and individuals who are part of an HD family
• relate phenotypical characteristics (genetic modifiers / wet and dry biomarkers)
• expedite identification and recruitment of participants for clinical trials
• develop and validate sensitive and reliable outcome measures for detecting onset and change over the natural course of premanifest and manifest HD which may also be potential outcome measures for use in future clinical trials and clinical care
• plan for future research studies

REGISTRY integrates prospectively and systematically collected clinical research data (e.g. phenotypical clinical features, family history, demographical characteristics) with access to biological specimens (e.g. blood, urine) obtained from individuals with manifest HD, unaffected individuals known to carry the HD mutation or at risk of carrying the HD mutation, and control research participants (e.g. spouses, siblings or offspring of HD mutation carriers known not to carry the HD mutation).

REGISTRY is an open-ended study and eligible subjects are assessed at annual study visits on the phenotypical characteristics of HD regardless of whether they display clinical symptoms and signs of the disease and of individuals who are part of an HD family (irrespective of their mutation carrier status). At each study visit, general clinical, motor function, behavior, cognitive, Health Economics, Quality of Life assessments are administered. In addition, participants are given the option to consent to the donation of biosamples for the purposes of mutation (CAG repeat length) testing and for research to identify biological modifiers and markers of HD. Biological specimens and phenotypical data are made available to qualified scientists whose projects are reviewed and approved by the Scientific and Bioethical Advisory Committee (SBAC) of EHDN. Successful applicants agree to accept the EHDN policies surrounding the use of the data/materials provided and publication of results (see data sharing and publication policies of EHDN, attached). Research projects should aim to advance scientific knowledge towards establishing clinically effective treatments that delay onset and/or slow the progression of the disease.

REGISTRY-HD participants include those who are willing to participate in regular (annual) evaluations conducted by the investigators and have a diagnosis of HD, are HD mutation carriers (but who do not meet criteria for a diagnosis of HD) or persons at risk for HD (first and second degree relatives of people affected by HD), are non-HD mutation carrier relatives. Spouses of participants may take part as REGISTRY-CONTROLS.

Inclusion Criteria:

The following individuals may be eligible to participate

• Individuals, confirmed HD mutation carrier
• Manifest HD, without mutation (CAG) testing
• HD family member at-risk, without CAG testing
• HD family member, non-HD mutation carrier
• REGISTRY-CONTROL participants: companion/individual without HD history
• REGISTRY-COMPANION (any of the above).

Exclusion Criteria:

• Participants who are unable to understand the study protocol or unable to give informed consent, and have no legal representative.
• Participants with choreic movement disorder other than HD. (EHDN provides a Registry-like tool to record findings in patients affected with choreatic movement disorders other than HD under the label "Neuroacanthocytosis"; www.euro-hd.net/html/na/registry).

Individuals with manifest HD, unaffected individuals known to carry the HD mutation or at risk of carrying the HD mutation, and control research participants (e.g., spouses, siblings or offspring of HD mutation carriers known not to carry the HD mutation)