Also, some reports have focused on research DNA methylation at the 5′ promoter regions of candidate genes according to the basis of hypothesis concerning the molecular mechanisms of AD as microtubule-associated protein tau, amyloid precursor protein (APP) and preseniline-1 genes in the frontal cortex and hippocampus of both control and AD cases at different Braak stages. This evidence concerns the gene PSEN1 and Alzheimer disease.