HTT and Huntington disease: Huntington’s disease (HD) is a neurodegenerative disorder in which abnormally long CAG repeat expansions in the first exon of the huntingtin (HTT) gene result in a mutant form of the gene (mHTT), which disrupts glial as well as neuronal physiology, leading to dysfunction first evident in neostriatal medium spiny neurons (MSNs) (1).