CYP51A1 and Alzheimer disease: Significant increases in expression of the cholesterol biosynthesis gene family, a proposed key process in AD etiology77, occur later in CPS (DHCR24, LBR, FDFT, HSD17B1, SC5D, CYP51A1, SQLE, and DHCR7) (Fig. 7e, middle, and Fig. 7g).