Mutational analysis of hemoglobin genes and functional characterization of detected variants, through in-silico analysis, in Pakistani beta-thalassemia major patients

Thalassemia is one of the most prevalent genetic disorders worldwide. The present study aimed to explore the mutational spectrum of all hemoglobin (HB) encoding genes and to identify the potentially damaging and pathogenic variants in the beta (β)-thalassemia major patients and thalassemia minor carriers of Southern Punjab, Pakistan. A total of 49 β-thalassemia major patients and 49 carrier samples were screened for the identification of HBA1, HBA2, HBB, HBD, HBE1, HBG1 and HBG2 variants by NGS. PCR was performed for the amplification of HB encoding genes and the amplified product of 13 patients and 7 carrier samples were processed for the Sanger sequencing. Various bioinformatics tools and databases were employed to reveal the functional impact and pathogenicity potential of the observed variants. Results depicted a total of 20 variants of HB-related genes by NGS and 5 by Sanger sequencing in thalassemia patients. While 20 variants by NGS and 3 by Sanger were detected in carriers. Few known genetic variants of HB-encoding genes are being reported for the first time in Pakistani thalassemia patients and carriers. However, two novel HBB variants c.375A>C (p.P125P) and c.*61T>G and a novel variant of HBE1 (c.37A>T (p.T13S)) were also documented. Pathogenicity analysis predicted the pathogenic potential of HBB variants (c.47G>A (p.W16*), c.27-28insG (p. S10fs), and c.92+5G>C) for β thalassemia. The study of functional impact indicated that these HBB variants result in the premature termination of translation leading to the loss of functional β-globin protein. It is therefore suggested that the pathogenic HBB variants, identified during present study, can be employed for the diagnosis, carrier screening, and planning therapy of thalassemia.