PLP1 and Alzheimer disease: The extent of reduction in MAG:PLP1 ratio and elevation of VEGF correlate with: (i) amyloid-β42 level28; (ii) the level of fibrinogen (associated with blood–brain barrier leakiness); (iii) the decline in platelet-derived growth factor receptor-β (PDGFRβ) (reflecting loss of pericytes within the brain in Alzheimer’s disease); and (iv) the concentration of endothelin-1 (EDN1),24 a potent vasoconstrictor peptide that we previously showed to be elevated in Alzheimer’s disease.30