HTT and Huntington disease: In the present study, specifically, we used STHdh Q7/7 and STHdh Q111/111 cell lines (which we refer to as Q7 and Q111, respectively, in figures) derived from a knock-in mouse model of HD and endogenously expressing full-length Htt with either short (Q7) or long (Q111) polyglutamine (polyQ) repeats25.