A study from Western Iran in β-thalassemia patients report the presence of Xmn1 polymorphic site on both chromosomes (+/+) the level of Hb F tended to be increased compared to the absence of Xmn1 ( / ) and the presence of this polymorphic site caused a positive influence on Hb F production and the Gγ percent which could improve the clinical symptoms of β-thalassemia patients.30 Our finding in sickle cell disease patients was similar with the study. Here, GSTM1 is linked to sickle cell disease.