In contrast, we were able to identify a shift in the relation between PO2 and HbO2, and variations in P50 value, in 55 patients with HbCO ≥8% (increased Hb affinity) and 30 patients with sickle cell disease (decreased Hb affinity, even more when they were not treated by hydroxycarbamide). This evidence concerns the gene GSTM1 and sickle cell disease.