The molecular characterization of Beta globin gene in thalassemia patients reveals rare and a novel mutations in Pakistani population.

INTRODUCTION: A multicentre study (including four cities in Pakistan) aimed to investigate the frequency and spectrum of alpha and beta thalassemia genetic mutations and XmnI polymorphism of the Gamma Globin gene. METHODS: One hundred and sixty one beta thalassemia patients, identified on the ground of haematological parameters, were screened for mutations of the Alpha (HBA2 and HBA1) and Beta (HBB) Globin genes as well as Gamma (HBG2) Globin gene, -158 Gγ XmnI polymorphism, using a combination of multiplex GAP polymerase chain reaction (PCR), Sanger sequencing and restriction fragment length polymerase (RFLP) based PCR. RESULTS: Mutations of at least one HBB gene was identified in 157 of 161 patients screened. Among 16 identified mutations in the beta gene, HBB:c.27_28insG (p. Ser10Valfs*14) was the most prevalent. α(-3.7) and α(-4.2) deletions were co-inherited with beta thalassemia mutations. Rare mutations such as HBB:c.-138C > T and HBB:c.315 + 1G > A were also identified. One novel variant (HBB:c.-148T > A), two rare mutations [HBB:c.332T > C (p.Leu111Pro); HBB:c.92G > C (p.Arg31Thr] and a novel association, HBB:c.[92G > C (p.Arg31Thr)] and [-92C > G], were reported for the first time in our study. HBG2:c.-211C > T base-pair substitution (historically described as -158 GγXmnI polymorphism) was present in 36% of the patients. CONCLUSION: Heterogeneity in clinical and haematological parameters in TM, show that monogenic disorders can present with a wide spectrum of disease severity. Our studies identified rare and novel mutations that will be useful in the prevention of highly prevalent disease of thalassemia in Pakistan following nationwide awareness campaign.