We investigated HD modifier MMR genes and their cognate heterodimer partners by targeting MutS (MSH2, MSH3, and MSH6), MutL (MLH1, PMS1, PMS2, and MLH3), and LIG1 expression using a CRISPR interference system in HD induced pluripotent stem cells (iPSCs). The gene discussed is MRC1; the disease is Huntington disease.