Cystatin C is an accurate biomarker for the early detection of AKI, and may, in selected populations, be superior to creatinine; however, data have been inconsistent and Cystatin C is modified by age, sex, muscle mass, obesity, smoking status, thyroid function, inflammation, and malignancy [8]. The gene discussed is CST3; the disease is obesity due to melanocortin 4 receptor deficiency.