Motor outcome measures in Huntington disease clinical trials.

Deficits in motor function are a hallmark of Huntington disease (HD). The Unified Huntington's Disease Rating Scale Total Motor Score (UHDRS-TMS) is a categoric clinical rating scale assessing multiple domains of motor disability in HD. The UHDRS-TMS or subsets of its items have served as primary or secondary endpoints in numerous clinical trials. In spite of a well-established video-based annual online certification system, intra- and interrater variability, subjective error, and rater-induced placebo effects remain a concern. In addition, the UHDRS-TMS was designed to primarily assess motor symptoms in manifest HD. Recently, advancement of technology resulted in the introduction of the objective Q-Motor (i.e., Quantitative-Motor) assessments in biomarker studies and clinical trials in HD. Q-Motor measures detected motor signs in blinded cross-sectional and longitudinal analyses of manifest, prodromal, and premanifest HD cohorts up to two decades before clinical diagnosis. In a multicenter clinical trial in HD, Q-Motor measures were more sensitive than the UHDRS-TMS and exhibited no placebo effects. Thus, Q-Motor measures are currently explored in several multicenter trials targeting both symptomatic and disease-modifying mechanisms. They may supplement the UHDRS-TMS, increase the sensitivity and reliability in proof-of-concept studies, and open the door for phenotype assessments in clinical trials in prodromal and premanifest HD.