MSH3 and juvenile Huntington disease: Further, genome-wide association studies (GWASs) for the age of onset and progression of Huntington's disease have identified mutations in MLH1 (Genetic Modifiers of Huntington's Disease (GeM-HD) Consortium 2015) and MSH3 (Moss et al. 2017) that lead to increased somatic instability of the pathogenic trinucleotide expansion at HTT, and MSH3 is a current drug target for Huntington's disease (Kingwell 2021).