GSTM1 and sickle cell disease: The first descriptions of haematological response to hydroxyurea in HbSC disease were published 25 years ago [30] when it was noted in a small case series (6 patients) that low dose hydroxyurea (10–20 mg/kg/day) increased the Hb, MCV, and HbF while decreasing neutrophils and reticulocytes.