Zinc finger polypeptides comprising from 8 to 23 zinc finger domains. The polypeptides may also comprise the human KRAB repressor domain from Kox-1 or the mouse KRAB repressor domain from ZF87. Also claimed is an adeno-associated virus (AAV) vector comprising a nucleic acid expression construct capable of expressing the zinc finger polypeptides. The polypeptides exhibit reduced immunotoxity in vivo and may have utility in sustained (mid- or long-term) expression in vivo and may be use in treating polyglutamine diseases such as Huntingtons disease.