HTT and Huntington disease: To investigate both mechanisms underlying HD, mutHTT GoF and wtHTT LoF, we used a cell line endogenously expressing mutHTT together with the wtHTT allele (named HD), control lines expressing normal HTT (named IC1 and IC2, which express one and two wtHTT alleles, respectively), and an HTT-knockout line (named KO) (Fig. 1a) [32].