We here tested whether there is a causal relationship between cystatin C and risk of CAD using a Mendelian randomization approach by testing whether genetic elevation of cystatin C, measured by a SNP at the cystatin C locus on chromosome 20 robustly associated with plasma cystatin C (rs13038305), alters the risk of CAD in more than 25 000 cases of CAD and almost 90 000 control subjects. The gene discussed is CST3; the disease is coronary artery disorder.