C9orf72 and Huntington disease: It included specific diseases (i.e., ALS, FTD, HD, FXTAS) and related pathological mechanisms (i.e., RAN translation, C9orf72 hexanucleotide repeat, antisense transcript, nucleocytoplasmic transport, CAG repeats, RNA foci, antisense RNA, CGG repeats, and liquid-liquid phase separation).