Mutation Pattern in Beta Thalassaemia Trait Population: A Basis for Prenatal Diagnosis

A total of 100 Bangladeshi beta thalassaemia carrier subjects were analysed by allele specific primers using Amplification Refractory Mutation System – Polymerase Chain Reaction.  Among these, four common mutations were found in 90 cases (90.0%), five less common mutations in 9 cases (9.0%) and a rare mutation in 1 case (1.0%). Among the four common mutations, IVS1-5 (G-C) was the most common beta thalassaemia mutation and found in 63.0% cases, followed by Cd 30 (G-C) in 18.0%, Fr 8/9 (+G) in 5.0% and Fr 41/42 (-TTCT) in 4.0% respectively. Among the five less common mutations, Cd16 (-C) was found in 3.0%, -90 (C-T) and IVS1-130 (G-C) were seen in 2.0% each and remaining Cd15 (-T) and Cd15 (G-A) were detected in 1.0% each. The rare mutation was -29 (A-G), observed in one case (1.0%). With the application of this knowledge, it will help us for prenatal diagnosis and genetic counselling in Bangladesh for prevention of the disease.

High resolution melting curve analysis targeting the HBB gene mutational hot-spot offers a reliable screening approach for all common as well as most of the rare beta-globin gene mutations in Bangladesh

BACKGROUND

Bangladesh lies in the global thalassemia belt, which has a defined mutational hot-spot in the beta-globin gene. The high carrier frequencies of beta-thalassemia trait and hemoglobin E-trait in Bangladesh necessitate a reliable DNA-based carrier screening approach that could supplement the use of hematological and electrophoretic indices to overcome the barriers of carrier screening. With this view in mind, the study aimed to establish a high resolution melting (HRM) curve-based rapid and reliable mutation screening method targeting the mutational hot-spot of South Asian and Southeast Asian countries that encompasses exon-1 (c.1 - c.92), intron-1 (c.92 + 1 - c.92 + 130) and a portion of exon-2 (c.93 - c.217) of the HBB gene which harbors more than 95% of mutant alleles responsible for beta-thalassemia in Bangladesh.

RESULTS

Our HRM approach could successfully differentiate ten beta-globin gene mutations, namely c.79G > A, c.92 + 5G > C, c.126_129delCTTT, c.27_28insG, c.46delT, c.47G > A, c.92G > C, c.92 + 130G > C, c.126delC and c.135delC in heterozygous states from the wild type alleles, implying the significance of the approach for carrier screening as the first three of these mutations account for ~85% of total mutant alleles in Bangladesh. Moreover, different combinations of compound heterozygous mutations were found to generate melt curves that were distinct from the wild type alleles and from one another. Based on the findings, sixteen reference samples were run in parallel to 41 unknown specimens to perform direct genotyping of the beta-thalassemia specimens using HRM. The HRM-based genotyping of the unknown specimens showed 100% consistency with the sequencing result.

CONCLUSIONS

Targeting the mutational hot-spot, the HRM approach could be successfully applied for screening of beta-thalassemia carriers in Bangladesh as well as in other countries of South Asia and Southeast Asia. The approach could be a useful supplement of hematological and electrophortic indices in order to avoid false positive and false negative results.

Spectrum of Types of Thalassemias and Hemoglobinopathies: Study in a Tertiary Level Children Hospital in Bangladesh

Thalassemias and hemoglobinopathies are the most common hemolytic congenital disorders in Bangladesh as in many parts of the world. This study was done to find the common types of thalassemias and abnormal hemoglobin variants seen in Bangladeshi populations. A total of 4813 samples were analyzed for hemoglobin disorders out of which 2308 (49.95%) showed abnormalities. The samples were analyzed by Bio Rad D 10 Analyzer in 3914 (81.32%) cases, BIORAD VARIANTβ thalassemia short program using the principle of high performance liquid chromatography in 474 (9.85%) cases and by CAPILLARYS 2 FLEX PIERCING utilizing capillary electrophoresis in 425 (8.83%) cases. The samples were analyzed in the Department of Biochemistry and Molecular Biology of Dhaka Shishu (Children) Hospital, Dhaka, Bangladesh. The common hemoglobin disorders seen were β trait 863 (17.94%), Hb E trait 601 (12.50%), Hb E β thalassemia 524 (10.87%), β thalassemia major 192 (4.00 %), Hb E disease 99 (2.05%). Other Hb abnormalities detected were Hb D trait 17 (0.35%), Sickle cell trait 4 (0.08%), hereditary persistence of fetal hemoglobin (HPFH) 2 (0.04%), and Hb Lepore, δ β thalassemia, sickle cell β thalassemia, Sickle cell disease, compound heterozygote for HbE+D and Hb Q band one case each (0.02%).

Combination of two rare mutations causes β-thalassaemia in a Bangladeshi patient

Screening of mutations that cause β-thalassaemia in the Bangladeshi population led to the identification of a patient with a combination of two rare mutations, Hb Monroe and HBB: −92 C > G. The β-thalassaemia major male individual was transfusion-dependent and had an atypical β-globin gene cluster haplotype. Of the two mutations, Hb Monroe has been characterized in detail. Clinical effects of the other mutation, HBB: −92 C > G, are unknown so far. Bioinformatics analyses were carried out to predict the possible effect of this mutation. These analyses revealed the presence of a putative binding site for Egr1, a transcription factor, within the HBB: −92 region. Our literature survey suggests a close relationship between different phenotypic manifestations of β-thalassaemia and Egr1 expression.

Mutation analysis of the HBB gene in selected Bangladeshi beta-thalassemic individuals: presence of rare mutations

INTRODUCTION AND AIMS

Bangladesh has a large number of thalassemic patients. However, no extensive analysis of the mutations in the HBB gene of thalassemic patients has been previously carried out. We have conducted a systematic research to reveal thalassemia mutations in the Bangladeshi population. In this preliminary analysis of 587 bp of the HBB gene in selected thalassemic individuals, some rare mutations in world perspective have been found to be significantly high in the Bangladeshi population, together with the common mutations for thalassemia.

RESULTS

A 587-bp segment of the HBB gene from 32 chromosomes of 16 beta-thalassemic individuals was analyzed for molecular characterization of the disease. Splice junction mutation IVS-I-5 was found to be the most common. The analysis also revealed some rare mutations HBB: c.-80T>C, HBB: c. 92G>C, HBB: c-92C>G, which are not prevalent in geographically adjacent populations.

CONCLUSION

This is a first of this kind of study in the Bangladeshi population. Although the small sample size makes it difficult to make any population genetics inference, this study can be regarded as the seminal research for a large-scale study to determine the complete mutation profile underlying thalassemia in the Bangladeshi population. The complete mutation profile will provide invaluable strategies (e.g., prenatal diagnosis and genetic counseling) for better management of thalassemia in the Bangladeshi population.

Fatal sepsis due to Pseudomonas cepacia

Pseudomonas cepacia is known as an opportunistic pathogen in the patients with altered host defence. We report a case of hospital-acquired fatal sepsis due to P. cepacia in a child with no known defect in immune system. Virulence of the organism was indicated by the high magnitude of septicaemia. The organism was successfully eliminated by ceftriaxone but the patient died of renal failure.