Impacts of pathogenic mutations and XmnI polymorphism on the severity of haemoglobin E β-thalassaemia patients in Bangladesh

Abstract

Background: Haemoglobin E β-thalassaemia is a common blood disorder in South Asia, especially Bangladesh. The disorder can range from mild and asymptomatic anemia to life-threatening anemia. Patients with asymptomatic anemia do not require blood transfusions in their lifetime. Mild Hb E beta thalassaemia patients require occasional blood transfusions. However, patients with life-threatening anemia need frequent blood transfusions. The presence of XmnI polymorphism with specific mutation led to a delay of blood transfusions, higher haemoglobin levels, better response to hydroxyurea treatment, and milder phenotypic presentation among Hb E β thalassaemia patients. Aims: The aim of this study is to examine how the HBB gene mutations and the XmnI polymorphism affect the severity and transfusion needs of haemoglobin E β thalassaemia patients. Methodology: In this study, a total of 360 Hb E β-thalassaemia patients were included. The seven common HBB mutations in Bangladesh were detected by amplification refractory mutation system (ARMS) method, and rare/novel mutations were detected by Sanger sequencing. Moreover, XmnI (PdmI) restriction site was detected by XmnI (PdmI) restriction enzyme digestion. Results: Among the subjects in this research, 62.5% (n=225) were regular transfusion dependent, 22.8% (n=82) were occasionally transfusion-dependent, 8.1% (n=29) were one-time transfusion patients, and 6.7% (n=24) were transfusion-independent patients. This study identified a total of thirteen pathogenic mutations among the 360 Hb E β thalassaemia patients. The most common mutation was IVS 1-5 (G>C), accounting for 57.8% (n=208) of cases, followed by Fr 41/42(-CTTT) 12.2% (n=44), codon 30 (G>C) 8.3% (n=30), Fr 8/9 (+G) 7.5% (n=27), codon 16 (-C) 3.9% (n=14), and codon 15 (G>A) 2.8% (n=10). The study also identified six rare mutations, including -90(C>T) 3.1% (n=11), IVS-I-130(G>A) 3.1% (n=11), IVS II-654 (C>T) 0.6% (n=2), and -30 (T>C) 0.3% (n=1), codon 14/15 (+G) 0.3% (n=1) and -29 (A>G) 0.3% (n=1). Of these, -29 (A>G) had not been reported previously in Bangladesh. Page | v This study found that those with codon 16 (-C) mutation required regular transfusions, while those with codon 30 (G>C) mutations had the least transfusion dependency (6.7%). Patients with codon 30 (G>C) mutations had the highest response to hydroxyurea therapy (76.7% (n=23)) (p=0.051), while patients with Codon 16 (-C) mutations had the lowest response (0% (n=14)) (p=0.057). Codon 16 (-C) mutation was associated with the least HbF (mean ± SD= 24.8±7.7%), while codon 30 (G>C) mutation was associated with the highest HbF (mean ± SD= 41.9±16.10%). Regarding XmnI polymorphism, Codon 16 (-C) mutation was associated with the highest wild type (-/-) (n=11) genotype (p=0.153), while codon 30 (G>C) mutation was associated with the highest homozygous mutated (+/+) (n=11) and the least wild type (-/-) (n=4) of XmnI polymorphism genotype (p=0.157). Conclusion: The outcomes of this study will be useful for developing treatment strategies involving HU therapy and for managing Hb E β-thalassemia patients in Bagladesh.