Enabling routine β-thalassemia Prevention and Patient Management by scalable, combined Thalassemia and Hemochromatosis Mutation Analysis

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.

Frequency of Hereditary Hemochromatosis Gene (HFE) Variants in Sri Lankan Transfusion-Dependent Beta-Thalassemia Patients and Their Association With the Serum Ferritin Level

INTRODUCTION

Co-inheritance of hereditary hemochromatosis (HFE) gene variants p. C282Y and p.H63D worsen iron overload in transfusion-dependent thalassemia. Data on the HFE gene variants in Sri Lankan patients with thalassemia have not been extensively studied. This study aimed to analyze the p.C282Y and p.H63D variants in transfusion-dependent beta (β) and HbE/β-thalassemia patients and establish an association between these variants and their serum ferritin levels.

MATERIALS AND METHODS

A total of 125 transfusion-dependent β-thalassemia major and HbE/β thalassemia patients were tested for the c.845G>A (p.C282Y) and c.187C>G (p.H63D) HFE gene variants using the multiplex Amplification Refractory Mutation System Polymerase Chain Reaction method. For phenotype-genotype correlation, serum ferritin levels, the erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels were measured. The standard descriptive statistics were used for data analysis.

RESULTS

The study cohort consisted of transfusion-dependent 123 β-thalassemia and 2 HbE/β-thalassemia patients. The p.C282Y variant was not detected in any patient; allele frequency for the wild type (c.845GG) was 100%. Twenty-three patients were heterozygous for the p.H63D variant allele, and the allele frequencies were c.187CC 91.8%, c.187CG 9.2%, and c.187GG 0%. The mean serum ferritin level was relatively higher (mean level 4,987 ng/ml) in the p.H63D heterozygous (c.187CG) group compared to the wild type (c.187CC) group (mean level 4,571 ng/ml), but the difference was statistically not significant (p = 0.865). Among the total study population, CRP, ESR, and serum glutamine aspartate transaminase (SGPT) were elevated in 9 (7.2%), 65 (52%), and 82 (65.6%) patients, respectively. Among the p.H63D c.187CG group, elevated CRP, ESR, and SGPT were present in 5 (5%), 15 (12%), and 18 (14.4%) patients, respectively. The detected sample number was low to correlate with the confounding effect of inflammatory disorders and liver damage on the serum ferritin levels.

CONCLUSIONS

The HFE gene variant p.C282Y is unlikely to cause iron overload in the Asian β-thalassemia patients; the rarity of this variant in the study cohort replicates the findings of other South Asian population studies of this variant. The presence of the p.H63D variant could be a potential risk factor for iron overload in the β-thalassemia patients. A more extensive cohort study is required to validate this finding.