Impairment of DNA methylation has already been shown to have a relationship with neural development and neurodegenerative diseases, in studies in primates and rodents, lack of dietary B-vitamins or excessive exposure to metals (lead) early in development can affect DNA methylation levels in vivo, resulting in changes in Aβ peptide gene expression associated with the pathogenesis of AD, such as BACE1, PSEN1, and APP genes (Fuso et al., 2005, 2011; Bihaqi et al., 2011). Here, PSEN1 is linked to Alzheimer disease.