Given the role of CYP27A1 in cholesterol efflux and BAs synthesis, we investigated the effect of Cyp27a1 deficiency on the development of atherosclerosis in Apolipoprotein E (ApoE) knock out (KO) mice, anticipating that atherosclerotic lesions would be increased in Cyp27A1 KO/ApoE KO double knockout (DKO) mice. Here, APOE is linked to atherosclerosis.