Development of Assessments for Later Stage HD

The primary objective of this study is to evaluate the internal consistency, reliability and validity of two assessments: (1) UHDRS Structured Interview of Function (SIF) that incorporates the UHDRS Total Functional Capacity, Functional Assessment Scale, and Independence Scale (UHDRS TFC, FAS and IS), and (2) the HD Clinical Status Questionnaire (HDCSQ). There will be two study parts: Part 1 will measure the performance of the UHDRS SIF assessment compared to the original UHDRS TFC, FAS and IS using a cross-over design by collecting data from the Manifest HD gene expansion carrier participants (Manifest HDGEC Participants) and their companions (Companion Participants) via an in-person baseline visit and a follow-up visit by phone. Part 2 will assess the UHDRS SIF and the HDCSQ using a cross-sectional design by collecting data from the Companion Participants via a follow-up visit by phone. Participants of Part 1 are eligible to participate in Part 2.