The purpose of this study is to collect prospective data from individuals who are part of a Huntington Disease (HD) family, in order to relate phenotypes between individuals and families with each other and genetic factors in order to learn more about HD, develop potential treatments for HD, and to plan for future research studies of experimental drugs aimed at slowing or postponing the onset and progression of HD.

COHORT (Cooperative Huntington Observational Research Trial) is a coordinated research effort by Huntington Study Group research centers worldwide to prospectively collect data from consenting individuals who are affected by Huntington's disease (HD) and who are part of an HD family. The systematically accrued data from annual prospective assessments will relate clinical characteristics (phenotypes) between families with genetic and environmental factors. The knowledge from these relationships will better inform us about the onset and progression of HD, help identify potential interventions for HD, and aid in planning research studies of experimental treatments aimed at slowing or postponing the onset of HD. The consented collection of biological samples will further provide research material and correlative data for scientists to identify biomarkers that parallel the development and progression of HD. Identification of biomarkers will in turn contribute to our understanding of HD and enhance the efficiency and power of disease-modifying therapeutic trials.

Inclusion Criteria:

• (1) MANIFEST/PRE-MANIFEST HD: Individuals of any age who are affected by HD OR an individual 18 years or older who - has tested positive for the HD gene.
• (2) INDIVIDUALS AT RISK: An individual 18 years or older who has not undergone DNA testing for the mutation responsible for HD and who is a first degree relative (parent, sibling, child) of an individual with Manifest or pre-manifest HD OR an older adolescent 15 to 17 years of age who has a parent with manifest HD or pre-manifest HD enrolled in COHORT.
• (3) ADULTS AT SECONDARY RISK: An individual 18 years of age or older who has not undergone DNA testing for the mutation responsible for HD and is a grandparent or grandchild of an individual enrolled in COHORT who has manifest HD or pre-manifest HD
• (4) CONTROL: A spouse or caregiver, 18 years of age or older, of an individual enrolled in COHORT who has manifest HD or pre-manifest HD
• (5) ADULT GENE NEGATIVE: An individual, 18 years of age or older, with a family history of HD who has undergone DNA testing and does not carry the genetic mutation responsible for HD.

Exclusion Criteria:

• (1) Anyone who does not fit the inclusion criteria

1. An individual of any age that is affected by Huntington's disease
2. An individual 18 years of age or older, who has tested positive for the HD gene
3. An individual 18 years of age or older who is a parent, sibling or child of an individual affected by HD
4. An older adolescent 15 to 17 years of age, who has a parent affected by HD enrolled in COHORT, or a parent who has tested positive for the HD gene enrolled in COHORT (at select sites)
5. Grandparents and grandchildren of anyone participating in COHORT who fulfills the requirements of (the above) category (1) or (2)
6. HD family members who have no risk for HD due to no family history (spouses or caregivers)
7. HD family members who have undergone DNA testing and does not carry the genetic mutation responsible for HD.