GSTM1 and malaria: Clinically, the study participants were classified into two categories based on a previous study in an age- and geographically-defined reference population from western Kenya [25], i.e., severe malaria anemia (SMA; Hb < 6.0 g/dL; n = 114) and non-SMA (Hb ≥ 6.0 g/dL, n = 160).