GSTM1 and anemia (phenotype): Anemia in infancy may be defined relatively as any value for the hemoglobin [Hb] less than two standard deviations (<–2σ) below the mean for age [33], or absolutely as less than a fixed value, such as 13.5 g/dL which is the −2σ level below mean cord blood Hb and mean Hb at 1 week [34].