BDNF and Alzheimer disease: Indeed, increased levels of BDNF promoter gene methylation were observed in the peripheral blood of MCI patients compared to control subjects, and were also increased in the MCI patients who converted to AD compared with the non-conversion group at the 5-year follow up point, thus suggesting that peripheral BDNF methylation could serve as an epigenetic biomarker for predicting the conversion from MCI to AD [54].