UGT1A1 and alpha thalassemia spectrum: We first excluded the potential coinfluence of alpha thalassemia and βs genotype on UGT1A1 (Table 3a and 4a) since these factors can significantly modify the substrate load on UGT1A1. As shown in Table 2 the UGT1A1 polymorphism influences only, but highly significantly, the serum total bilirubin level.