Interestingly, the deoxyribonucleoside analog FdCyd, but not the ribonucleoside analogs, zebularine and 5-azacytidine, demonstrated neuroprotective effects against mutant Htt-induced toxicity in primary cortical neurons in cell viability and neurite degeneration assays (Fig. 1F,G, and S3A–C), suggesting that the deoxyribonucleoside form of DNMT inhibitors, which act directly through DNA, exerts neuroprotective activity in HD neurons. This evidence concerns the gene DNMT1 and Huntington disease.