The reported prevalence of renal dysfunction in the Fontan population varies between 10% and 50% depending on the study population and whether estimated glomerular filtration rate (eGFR) is calculated with creatinine or muscle mass-independent cystatin C.5Previous studies on Fontan-associated nephropathy were limited to a cross-sectional setting, prohibiting an accurate evaluation of the course of renal function over time. The gene discussed is CST3; the disease is Abnormal renal physiology.