This high prevalence among children and pregnant women is further complicated by the occurrence of two specific forms of anemia that have been observed exclusively in these groups: “physiological anemia” and “pathological anemia.” In pregnant women, “physiological anemia” is caused by a hemodilution process, leading to Hb values below the threshold defined by the WHO, although this condition is considered normal. The gene discussed is GSTM1; the disease is anemia.