RXRA gene variations influence Alzheimer's disease risk and cholesterol metabolism

Cholesterol metabolism is altered in Alzheimer's disease (AD). The nuclear hormone receptor Retinoic X Receptor a (RXRa) is a member of the nuclear ligand-activated transcription factor family. RXRs are key regulators of cholesterol synthesis and thus cholesterol metabolism. We performed a systematic screen for gene variants in the RXRA gene. The effect of these gene variants on the risk of AD was investigated in 405 AD patients (mean age: 74.27 +/- 9.37 years; female 78.6%) and 347 controls (mean age: 73.26 +/- 8.37 years; female 57.2%). Furthermore, the influence of RXRA gene variants on CSF and plasma levels of cholesterol, lathosterol and 24S-hydroxycholesterol were evaluated. One of the identified seven SNPs in RXRA influenced AD risk in our single marker analysis (rs3132293: P = 0.006). Haplotype analysis identified a three-marker haplotype (TGC) consisting of rs3118570, rs1536475 and rs3132293, which decreased the risk of AD (P = 0.009). The single marker rs3132293 (P = 0.026) and the TGC haplotype (P = 0.026) influenced CSF lathosterol levels in non-demented controls, and cholesterol levels in the combined sample comprising AD patients and controls (Rs3132293: P = 0.050; TGC haplotype: P = 0.035). 24S-Hydroxycholesterol CSF and plasma levels were also influenced by rs3132293 (CSF: P = 0.004; plasma: P = 0.001) and the TGC haplotype (CSF: P = 0.004; plasma: P = 0.002); this effect was most pronounced in AD patients (rs3132293: CSF: P = 0.009, plasma: P = 0.002; TGC haplotype: CSF: P = 0.019, plasma: P = 0.005). Our results suggest that RXRA gene variants might act as risk factor for AD via an influence on cerebral cholesterol metabolism.