Role of XmnI polymorphism in HbF induction in HbE/β and β-thalassaemia patients

Kaiissar Mannoor, Mohabbat Hossain, Farjana Akther Noor, Golam Sarwer Bhuyan, Syeed Saleheen Qadri
2019 Bangladesh Medical Research Council Bulletin  
Thalassaemia is one of the most common genetic blood disorders worldwide. Patients with β-thalassaemia major and HbE/β-thalassaemia are blood transfusion dependent. Foetal haemoglobin or HbF can play a role in disease manifestations in these patients and there is evidence that a homozygous state for XmnI polymorphic site, associated with increased expression of Gγ-gene, may play an important role among other factors in ameliorating the clinical severity of homozygous β-thalassaemia and
more » ... saemia and thalassaemia intermedia. The aim of this review was to provide a comprehensive review of the role of XmnI polymorphic site for increased HbF production in HbE/β and β-thalassaemia patients. Methods: Published literatures were reviewed on the allelic frequency of Xmn1 polymorphism and its effect on HbF induction among thalassaemia patients of different countries. Results: In all β-thalassaemias, Hb F levels are relatively increased due to the selective survival of the erythroid precursors that synthesize relatively more γ-chains. The expression of HbF level is dominated by three different loci: HBG2: γ -158C>T, BCL11A, and HBS1L-MYB intergenic region. Genetic determinants influencing Hb F response can be within the β-globin complex or trans-acting. The published literature showed that the C>T substitution (rs7482144) at position –158 of the Gγ-globin gene, referred to as the XmnI-Gγ polymorphism, is a common sequence variant in all population groups, present at a frequency of 0.32 to 0.35. It was found in some studies, response to Hydroxyurea (HU) has been shown to be largely associated with the presence of the C>T polymorphism at -158 XmnI site (HBG2:c.- 53-158C>T) upstream of the Gγ-globin gene and HU therapy exerts a 2- to 9- fold increase in γ-mRNA expression in β-thalassaemia patients. Conclusion: A number of various study groups around the world suggests that XmnI polymorphism is an important key regulator of disease severity of HbE/β and β-thalassaemia patients.
doi:10.3329/bmrcb.v45i3.44642 fatcat:bexgufvuw5exjdv2324qu5snna