The spectrum of beta-thalassemia mutations in Azerbaijan

Molecular and geographical heterogeneity of hemoglobinopathy mutations in Azerbaijanian populations

With the carrier rate of 4%-8.6%, β-thalassemia is one of the most prevalent hereditary disorders in Azerbaijan. Taking into consideration the high frequency of β-thalassemia as well as the occurrences of several other hemoglobinopathies, we conducted a large genotyping study to investigate the mutational background of common hemoglobinopathies in the country. Α- and β-globin genes were evaluated in the carriers of mutations identified via hematological indices and hemoglobin fractions (n = 1,757). Genotyping of β-thalassemia carriers identified through population screening revealed 32 mutations, with codon 8 [-AA]-34.96%, IVS-II-1 [G > A]-16.35%, and IVS-I-110 [G > A]-10.12% leading the spectrum. Analysis of associations of β-thalassemia mutations with geographical regions of the country identified the strongest association between codon 8 [-AA] and Shaki-Zaqatala, and codon 5 [-CT] in Mountainous Shirvan regions (ri > 6.00; p < 0.05). HbS, HbD-Punjab, and HbE were the most prevalent among our variant hemoglobin cohort, commonly inherited in compounds with β-thalassemia than in the homozygous state. We identified nine α-thalassemia mutations, 20.5 kb and 3.7 kb deletions together accounting for 74% of the spectrum. Point mutations of α-thalassemia were less common among our observations and were mainly inherited in compounds with deletions. Our results allow a better understanding of the wide spectrum of mutations in Azerbaijan and highlights the high heterogeneity of hemoglobinopathies in the local population.

Codon 14 (+T) (HBB: c.44_45insT): a Rare β-Thalassemia Mutation Reported Only in Azerbaijan

Codon 14 (+T) (HBB: c.44_45insT) is a very rare β-thalassemia (β-thal) mutation previously reported in three β-thal major (β-TM) patients of Azerbaijani origin. None of the previous reports described the genotype-phenotype correlation of the mutation. We here report the first case of homozygous codon 14 together with data of the heterozygous parents.

β-Thalassemia Haplotypes in Romania in the Context of Genetic Mixing in the Mediterranean Area

The purpose of this meta-study was to investigate β-thalassemia (β-thal) mutations and their chromosomal background in order to highlight the origin and spread of thalassemia alleles in the European and Mediterranean areas. Screening of more than 100 new Romanian β-thal alleles was also conducted. The results suggest an ancient introduction of mutations at codon 39 (C > T) (HBB: c.118C > T) and IVS-I-6 (T > C) (HBB: c.92 + 6T > C) in Romania. A comparative study was performed based on restriction fragment length polymorphism (RFLP) haplotypes associated with β-thal mutations in Romania and in Mediterranean countries. Each common β-thal allele from different populations exhibits a high degree of haplotype similarity, a sign of a clear unicentric origin for the IVS-I-110 (G > A) (HBB: c.93-21G > A), IVS-I-6, IVS-II-745 (C > G) (HBB: c.316-106C > G) and codon 39 mutations (the 17a [+ - - - - + +], 13c [ - + + - - - +], 17c [ + - - - - - +] and 14a [- + + - + + + ] ancestral RFLP background, respectively), followed by recurrent recombination events. This study also showed that geographic distances played a major role in shaping the spread of the predominant β-thal alleles, whereas no genetic boundaries were detected between broad groups of populations living in the Middle East, Europe and North Africa. The analyses revealed some discrepancies concerning Morocco and Serbia, which suggest some peculiar genetic flows. Marked variations in β(A) were observed between Southeast Asia and the Mediterranean, whereas a relative genetic homogeneity was found around the Mediterranean Basin. This homogeneity is undoubtedly the result of the high level of specific historic human migrations that occurred in this area.

The population genetics of the haemoglobinopathies

The haemoglobinopathies are the commonest single-gene disorders known, almost certainly because of the protection they provide against malaria, as attested by a number of observations. The geographical distributions of malaria and haemoglobinopathies largely overlap, and microepidemiological surveys confirm the close relationship between them. For two of the commonest disorders, haemoglobin S and alpha(+)-thalassaemia, there is also good clinical evidence for protection against malaria morbidity. However, not all the evidence appears to support this view. In some parts of the world malaria and haemoglobinopathies are not, and never have been, coexistent. It is also difficult to explain why the majority of haemoglobinopathies appear to be recent mutations and are regionally specific. Here we argue that these apparent inconsistencies in the malaria hypothesis are the result of processes such as genetic drift and migration and of demographic changes that have occurred during the past 10,000 years. When these factors are taken into account, selection by malaria remains the force responsible for the prevalence of the haemoglobinopathies.