Clinical 18F-fluoro-deoxygluose (FDG) Positron Emission Tomography (PET) studies also demonstrate reduced cerebral glucose metabolism (CMRglc) early in the course of AD [26, 27], especially among women at risk for AD [10, 28–32] and asymptomatic APOE4 carriers [33–36]. This evidence concerns the gene APOE and Alzheimer disease.