In an untreated patient with iron deficiency, 2 initial laboratory patterns may suggest an IRIDA diagnosis: 1) very low MCV (range: 45-65 fL) relative to the degree of anemia (Hb range: 60-80 g/L); and 2) marked hypoferremia and low transferrin saturation (usually <5%) in the presence of a slightly low or even normal serum ferritin level. The gene discussed is GSTM1; the disease is anemia (phenotype).