Variability of hemoglobin F expression in hemoglobin EE disease: hematological and molecular analysis

Although the molecular basis of variability of hemoglobin (Hb) F has been extensively examined in β-thalassemia and sickle cell diseases, less study has been done on Hb E disorder. To address the variability of Hb F expression in Hb EE disease, we have examined multiple single nucleotide polymorphisms (SNPs) in the β-globin gene cluster, BCL11A and HBS1L-MYB genes and determined their associations with Hb F levels in this syndrome. Study was done on 141 adult Thai individuals with homozygous Hb E. Hematological parameters were recorded and Hb F measured using Hb-HPLC analyzer. It was found in 26 cases that co-inheritance of α-thalassemia could lead to significant lower production of Hb F. Association of Hb F expression with the (G)γ-Xmn I polymorphism and other SNPs including rs2297339, rs2838513, rs4895441 and rs9399137 in HBS1L-MYB gene and rs4671393 and rs11886868 in BCL11A gene was therefore analyzed in the remaining 115 cases without α-thalassemia. It was found that 4 of these 7 SNPs including (G)γ-XmnI polymorphism (rs7482144), HBS1L-MYB (rs4895441) and (rs9399137) and BCL11A (rs4671393) were significantly associated with higher proportions of subjects with high Hb F (Hb F≥5%). The result demonstrated that multiple genetic modifying factors including T allele of (G)γ-XmnI polymorphism (rs7482144), G allele of HBS1L-MYB (rs489441), C allele of HBS1L-MYB (rs9399137) and C allele of BCL11A (rs4671393) are associated with increased Hb F and in combination could explain approximately 80% of the variation of Hb F in Hb EE disease in Thai population. Other genetic factors regulating Hb F expression in this common genetic disorder remains to be elucidated.