These included fibroblasts from patients with HD, differentiated neurons with striatal characteristics from a panel of induced pluripotent stem cell (iPSC) lines from patients with HD and a full-length mutant HTT knock-in mouse model expressing a human mutant exon-1 with the expanded CAG repeat (approximately 220 repeats) within the native mouse huntingtin gene, zQ175/+ (Fig. 1a). This evidence concerns the gene HTT and Huntington disease.