The risks of converting post-hoc findings into primary outcomes in subsequent trials

Huntington’s disease (HD) is a devastating neurodegenerative condition caused by a triplet repeat expansion of the huntingtin gene (1). Although rare it is amongst the most frequent autosomal dominant causes of dementia, frequently affecting individuals in the most productive decades of their lives. Clinically, it is characterized by a classic triad of fluctuating neuropsychiatric symptoms, and progressive movement and cognitive disorders, accompanied by other symptoms such as weight loss and sleep impairment. It is severely debilitating, has a huge impact on quality of life and is fatal, with a median survival after motor onset of around a quarter of a century (2).