Knock-down of TET2 resulted in significant downregulation of RPA1, and simultaneous knockdown of TET1 and TET2 led to decreased APEX1 and RPA3 transcript levels in HD NSC cell lines compared to corresponding wt controls indicating that oxidation of the methyl group of 5mC by TET enzymes play a regulatory role in repair gene expression in HD [50]. This evidence concerns the gene APEX1 and Huntington disease.