HTT and Huntington disease: Indeed, the pathological hallmarks of C9orf72 and HD, TDP-43 and PolyQ aggregates respectively, can coexist in brain of HD patients with pathological HTT CAG repeat numbers and in vitro analyses have shown that mutant huntingtin (mHTT) favours the seeding properties of TDP-43.4,5,34 The neuropathological examination of one C9orf72 patient carrying IA-HTT revealed a typical picture of C9orf72 disease.