MAPT and Alzheimer disease: Hyperhomocysteinemia is widely acknowledged to be a risk factor of AD (Smith et al., 2018), which influences DNA methylation (Coppede, 2010), DNA repair (Bednarska-Makaruk et al., 2016), oxidative stress (Deep et al., 2019), amyloid β aggregation (Chung et al., 2016; Hoffman et al., 2018), tau phosphorylation (Sontag et al., 2014), vascular endothelial dysfunction (Esse et al., 2019; Wu et al., 2019), and the secretion of inflammatory mediators, especially tumor necrosis factor α, nuclear factor κB, interleukin 6 (IL-6), and IL-8 (Di Meco et al., 2019).