Our study had three unique features: (1) good baseline anemia management status with <20% of patients having Hb <10 g/dL, (2) low baseline total ESA use with a mean ESA dose of <6000 IU per week, and (3) we used individual-level data and adjusted for interobservation dependence of multiple measurements using mixed models. The gene discussed is GSTM1; the disease is anemia.