Anemia, defined as low blood hemoglobin (Hb) concentration (less than 11.0 g/dl for 6–59-month children, 11.5 g/dl for 5–11-year-old children, 12.0 g/dl for 12–14-year-old children and non-pregnant women (for age 15 years and above), 11.0 g/dl for pregnant women, and 13.0 g/dl for adult men (for age 15 years and above). The gene discussed is GSTM1; the disease is anemia (phenotype).