The absorption of cholesterol from the intestine plays an important role in determining the plasma level of cholesterol, a well-established risk factor for atherosclerosis cardiovascular diseases. Nevertheless, the molecular basis of the absorption process and its regulation are largely unknown. We identified two inbred mouse strains, C57BL/6J and castaneus (CASA/Rk), that differ in cholesterol absorption and plasma plant sterol levels, a surrogate measure of cholesterol absorption from the intestine. An inter-cross between these strains revealed a plasma plant sterol locus on chromosome 14, which peaked at 17cM with a maximum LOD score of 9.9. Construction and studies in one chromosome 14 congenic strain, designated 14DKK, with 40.5cM of CASA/Rk interval introgressed onto the C57BL/6J background confirmed the effect of this locus on plasma plant sterol levels and cholesterol absorption. Moreover, studies in 14DKK animals disclosed a modified ileum-liver signalling pathway that affects bile acid metabolism and is likely to explain the effect of this locus.The main purpose of this grant proposal is to discover the culprit gene(s) at the 14DKK interval that modify plasma plant sterol levels and cholesterol absorption. To achieve this goal we will fine-map causative genes through construction of sub-congenic mouse strains, apply high throughput expression studies, sequence genes in our interval and test the effect of candidate genes through over-expression and knockdown in cell cultures. The discovery of these genes may lead to the development of novel genetic markers of susceptibility to hyper-cholesterolemia and new targets for therapy of dyslipidemic states and coronary heart disease.