MAPT and Alzheimer disease: We have previously found that impaired brain glucose metabolism in AD probably lead to abnormal hyperphosphorylation of tau and neurofibrillary degeneration via down-regulation of tau O-GlcNAcylation, a post-translational modification of proteins with β-N-acetylglucosamine (GlcNAc; Liu et al., 2004, 2009).