BMAL1 and Alzheimer disease: •Rhythmic methylation of BMAL1 is altered in both AD brains and fibroblasts•E4 treatment with either 5-Aza-2′ deoxycytidine (DNA methyltransferase inhibitor) or S-adenosyl-methionine (methyl donor); NIH3T3 cells only ↑ methylation from methyl donor led to ↓ amplitude, longer periods, and phase delays in circadian rhythmicity; ↓ methylation from inhibitor led to shorter period length, advanced phase and ↑ amplitude