Shen et al. found that in 302 patients with T2DM and CTO, GFR estimated using serum cystatin C (GFRCYS) correlated more closely with coronary collateral Rentrop score than that estimated using serum creatinine either by creatinine-based MDRD formula (GFRMDRD) or by Chronic Kidney Disease Epidemiology Collaboration equation (GFREPI). The gene discussed is CST3; the disease is type 2 diabetes mellitus.