How does the Huntington's disease mutation damage cells?

Huntington's Disease (HD) is an autosomal dominant neurodegenerative condition with devastating consequences. HD is caused by the expansion of a CAG trinucleotide repeat stretch in the coding sequence of the HD gene that gives rise to a long polyglutamine tract in the huntingtin protein. How this mutated protein gives rise to the disease state is controversial. In this Perspective, I discuss the results of a new study on the effects of the mutated huntingtin protein in light of previous findings and suggest that the HD mutation damages cells by perturbing multiple parallel pathways by gain-of-function and possibly also dominant negative mechanisms.