All the patients had a degree of anemia before surgery, which worsened shortly after surgery despite minimizing intra-operative fluids, use of albumin, and using pediatric tube phlebotomy [Median ΔHb (pre-Hb-post-Hb): 1.13 mg/dL; Median ΔHct (pre-Hct-post-Hct): 2.3%]. The gene discussed is GSTM1; the disease is anemia.