For participation in this epidemiological study, a single-day visit at the study site is required. Participants will be recruited from Huntington Disease clinics, and they will be asked to answer questions regarding their demographics, including sex, age, race and ethnicity, and their medical and medication history. At the end of the visit, a blood sample will be drawn to allow testing with a sequencing assay that is specifically designed for phasing single nucleotide polymorphisms (SNPs) on the wild-type Huntington (wtHTT) and mutant Huntington (mHTT) alleles.

Inclusion Criteria:

• Have signed the Informed Consent Form (ICF)
• Aged 25 to 60 years, inclusive, at the time of signing the ICF
• Confirmation of Huntington Disease (HD) gene expansion mutation carrier status
• Confirmation of Total Functional Capacity (TFC) ≥9 and Total Motor Score (TMS) >6 within 12 months prior to signing the ICF
• Ability to tolerate blood draws

Exclusion Criteria:

• None

This epidemiological study will be conducted in ambulatory men and women aged 25 to 60 years old (inclusive) who carry the Huntington Disease (HD) gene expansion and meet the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score (TMS) and Total Functional Capacity (TFC) criteria for HD Integrated Staging System (HD-ISS) Stages 2-3.