Although some studies have found an association between cystatin C and BMI [9, 10], percent body fat [11], and diabetes [10], the CKD-EPI cystatin C equation (CKD-EPICys) has been shown to have advantages over creatinine-based eGFR equations in patients in whom muscle mass is abnormally high [12]. The gene discussed is CST3; the disease is diabetes mellitus.