HTT and Huntington disease: By comparing immortalized striatal precursor cells from wild type mice (STHdhQ7/Q7 cells) to precursor cells derived from heterozygous and homozygous HdhQ111 knock-in mice (STHdhQ7/Q111 and STHdhQ111/Q111 cells), differences in a variety of HD-related cellular pathways have been discovered or confirmed, for instance an involvement of huntingtin in calcium handling deficits and mitochondrial dysfunction7–11 or effects on various signalling cascades12–14.