Non-deletional alpha thalassaemia: a review

BACKGROUND

Defective synthesis of the α-globin chain due to mutations in the alpha-globin genes and/or its regulatory elements leads to alpha thalassaemia syndrome. Complete deletion of the 4 alpha-globin genes results in the most severe phenotype known as haemoglobin Bart's, which leads to intrauterine death. The presence of one functional alpha gene is associated with haemoglobin H disease, characterised by non-transfusion-dependent thalassaemia phenotype, while silent and carrier traits are mostly asymptomatic.

MAIN BODY

Clinical manifestations of non-deletional in alpha thalassaemia are varied and have more severe phenotype compared to deletional forms of alpha thalassaemia. Literature for the molecular mechanisms of common non-deletional alpha thalassaemia including therapeutic measures that are necessarily needed for the understanding of these disorders is still in demand. This manuscript would contribute to the better knowledge of how defective production of the α-globin chains due to mutations on the alpha-globin genes and/or the regulatory elements leads to alpha thalassaemia syndrome.

CONCLUSION

Since many molecular markers are associated with the globin gene expression and switching over during the developmental stages, there is a need for increased awareness, new-born and prenatal screening program, especially for countries with high migration impact, and for improving the monitoring of patients with α-thalassaemia.

The genetic basis of asymptomatic codon 8 frame-shift (HBB:c25_26delAA) β(0) -thalassaemia homozygotes

Two 21-year old dizygotic twin men of Iraqi descent were homozygous for HBB codon 8, deletion of two nucleotides (-AA) frame-shift β(0) -thalassaemia mutation (FSC8; HBB:c25_26delAA). Both were clinically well, had splenomegaly, and were never transfused. They had mild microcytic anaemia (Hb 120-130 g/l) and 98% of their haemoglobin was fetal haemoglobin (HbF). Both were carriers of Hph α-thalassaemia mutation. On the three major HbF quantitative trait loci (QTL), the twins were homozygous for G>A HBG2 Xmn1 site at single nucleotide polymorphism (SNP) rs7482144, homozygous for 3-bp deletion HBS1L-MYB intergenic polymorphism (HMIP) at rs66650371, and heterozygous for the A>C BCL11A intron 2 polymorphism at rs766432. These findings were compared with those found in 22 other FSC8 homozygote patients: four presented with thalassaemia intermedia phenotype, and 18 were transfusion dependent. The inheritance of homozygosity for HMIP 3-bp deletion at rs66650371 and heterozygosity for Hph α-thalassaemia mutation was found in the twins and not found in any of the other 22 patients. Further studies are needed to uncover likely additional genetic variants that could contribute to the exceptionally high HbF levels and mild phenotype in these twins.

Rapid detection of α-thalassaemia alleles of --(SEA)/, -α(3.7)/ and -α(4.2)/ using a dual labelling, self-quenching hybridization probe/melting curve analysis

OBJECTIVES

The aim of the study was to set up an alternative automatic molecular diagnostic method for deletional α-thalassaemia mutations without gel electrophoresis.

METHODS

Based on the sequence variation within the two Z boxes and melting curve analysis of dually labelled probes, a real-time PCR assay was developed and validated for the rapid detection of major α-genotypes (--(SEA)/αα, --(SEA)/-α(3.7), --(SEA)/-α(4.2), --(SEA)/--(SEA), -α(3.7)/-α(3.7) and -α(4.2)/-α(4.2)).

RESULTS

Samples with the -α(3.7)/-α(3.7), -α(4.2)/-α(4.2), --(SEA)/αα, --(SEA)/-α(3.7), --(SEA)/-α(4.2), and --(SEA)/--(SEA) genotypes could be clearly distinguished. The accuracy of this technique for these samples was 100% sensitivity and specificity.

CONCLUSION

This technique is rapid and reliable, demonstrating feasibility for use in large-scale population screening and prenatal diagnosis of deletional Hb H disease and Hb Bart's hydrops fetalis.

A two-layered classifier based on the radial basis function for the screening of thalassaemia

The thalassaemias are blood disorders with hereditary transmission. Their distribution is global, with particular incidence in areas affected by malaria. Their diagnosis is mainly based on haematologic and genetic analyses. The aim of this study was to differentiate between persons with the thalassaemia trait and normal subjects by inspecting characteristics of haemochromocytometric data. The paper proposes an original method that is useful in screening activity for thalassaemia classification. A complete working system with a friendly graphical user interface is presented. A unique feature of the presented work is the adoption of a two-layered classification system based on Radial basis function, which improves the performance of the system.