A G6PD-deficient individual with baseline haemoglobin level x g/dL who received 0.25 mg/kg of primaquine had a similar risk of severe anaemia (Hb < 7 g/dL) to an individual who had not received primaquine with a 1 g/dL lower (x − 1 g/dL) baseline haemoglobin level. The gene discussed is GSTM1; the disease is anemia.