Clinical trials in Huntington's disease: Interventions in early clinical development and newer methodological approaches.

Since the identification of the Huntington's disease (HD) gene, knowledge has accumulated about mechanisms directly or indirectly affected by the mutated Huntingtin protein. Transgenic and knock-in animal models of HD facilitate the preclinical evaluation of these targets. Several treatment approaches with varying, but growing, preclinical evidence have been translated into clinical trials. We review major landmarks in clinical development and report on the main clinical trials that are ongoing or have been recently completed. We also review clinical trial settings and designs that influence drug-development decisions, particularly given that HD is an orphan disease. In addition, we provide a critical analysis of the evolution of the methodology of HD clinical trials to identify trends toward new processes and endpoints. Biomarker studies, such as TRACK-HD and PREDICT-HD, have generated evidence for the potential usefulness of novel outcome measures for HD clinical trials, such as volumetric imaging, quantitative motor (Q-Motor) measures, and novel cognitive endpoints. All of these endpoints are currently applied in ongoing clinical trials, which will provide insight into their reliability, sensitivity, and validity, and their use may expedite proof-of-concept studies. We also outline the specific opportunities that could provide a framework for a successful avenue toward identifying and efficiently testing and translating novel mechanisms of action in the HD field.