PGP and Alzheimer disease: An increase in dolichol phosphate (without addition of the oligosaccharide) has been demonstrated in the brain of subjects with AD [36], which could lead to the accumulation of Aβ peptide [36], since it is related to the decrease in P-glycoprotein (P-gp), which participates as an ejector pump of this peptide across the blood–brain barrier (BBB) [37].