The Spectrum of α-Thalassemia Mutations in Kurdistan Province, West Iran

Hb SKMC and an unprecedented γδβ-thalassemia: first report from Iraq

BACKGROUND

Thalassemias are genetic disorders of globin chain synthesis. In Iraq, β-thalassemia is more prevalent than α-thalassemia. This study identifies two unpredicted globin gene mutations, a rare α-globin gene mutation (Hb SKMC) and a novel γδβ-thalassemia deletion.

METHODS

Over 2 years, the Genetics unit at PAR hospital in Erbil, northern Iraq processed 137 β-thalassemia and 97 α-thalassemia genetic testing requests. Three symptomatic thalassemia cases with unreported genotypes were identified. Proband-1α and proband-2α had Hb H disease, while proband-1β had severe transfusion-dependent β-thalassemia (TDT). Molecular studies included multiplex PCR, reverse hybridization, multiplex ligation-dependent probe amplification (MLPA), and globin gene sequencing.

RESULTS

The α-thalassemia probands exhibited moderate microcytic hypochromic anemia with irregular transfusions and splenomegaly. Hb H disease was confirmed by positive Hb H tests and high-performance liquid chromatography (HPLC). Molecular analysis revealed heterozygous -MED deletion in proband-1α and α2Poly-A2 mutation in proband-2α. Sequencing identified the Hb SKMC (HBA1:c.283_300+3dup) mutation in both probands. The β-thalassemia proband showed anemia and regular transfusions. Molecular studies detected the IVS1.110 G>A mutation and a novel γδβ-thalassemia deletion in compound heterozygous form. The maternal sample showed the IVS1.110 G>A mutation, and MLPA confirmed the γδβ-thalassemia deletion in the paternal sample.

CONCLUSION

These findings highlight the genetic diversity of thalassemias in the region and emphasize the importance of advanced molecular diagnostics in detecting rare mutations.

The Spectrum of α-Thalassemia Mutations in Syrian Patients

α-Thalassemia (α-thal) is a globally prevalent genetic disorder of hemoglobin (Hb) structure where the rate of α-globin chain synthesis is reduced or absent due to the presence of α-globin mutation(s). The aim of this study is to define the spectrum of α-globin gene mutations and evaluate their allele frequency in a group of α-thal carriers. A total of 55 individuals with possible α-thal patients were referred from the thalassemia centers in Syria. They have unexplained hypochromia and microcytosis. All patients were genetically tested for 21 common α-globin gene mutations using reverse hybridization kit. Seven different α-globin gene mutations and 13 different genotypes were detected in 55 patients. The two most frequently encountered mutations were -α3.7 deletion (47.1%) and --MED mutation (21.4%). The most commonly observed genotype was -α3.7/αα (40%), followed by --MED/αα genotype (21.8%). We determined the most common α thalassemia mutations in the Syrian patients. α-Thalassemia mutations with deletions were mostly observed in our study.

Problem of borderline hemoglobin A2 levels in an Iranian population with a high prevalence of α- and β-thalassemia carriers

Background

It is difficult to classify a small fraction of α- and β-thalassemia (α- and β-thal) carriers based on their Hb A2 levels. Here, we report the results of a molecular investigation in a cohort of thalassemia carriers with borderline Hb A2 levels originated from western Iran.

Results

The documents of 5956 α- or β-thal carriers were reviewed. The frequency of individuals with borderline Hb A2 levels in this cohort was 436 (7.32%). A total of 12 different α-thal and 27 different β-thal variants were identified in this study.

Conclusions

Our data showed that individuals with borderline Hb A2 are not uncommon in our population. Moreover, preselection of α- and β-thal carriers with borderline Hb A2 levels based on Hb A2, mean corpuscular volume (MCV), and mean cell hemoglobin (MCH) is not advisable in our population. Therefore, it is necessary to investigate both α- and β-globin genes in cases with borderline Hb A2 levels, especially if the partner is a carrier of β-thal or α0-thal.

In silico prediction of HBD gene variants in the Iranian population

Background

The quantification of hemoglobin A2 (Hb A2; α2δ2) is used as a valuable test to differentiate α- and ß-thal carriers in clinical laboratories. Therefore, the HBD (δ-globin) gene variants could result in reduced levels of Hb A2 and have implications for thalassemia screening programs. The aim of the present study was to predict the consequences of HBD gene variants identified in the Iranome project.

Results

The highest number of variants was in the Persian Gulf Islanders. The variants of p.Gln132Glu (HBD: c.394C>G), p.Gly17Arg (HBD: c.49G>C), p.Thr5Ile (HBD: c.14C>T), and p.Ala28Ser (HBD: c.82G>T) presented damage results in three or more prediction tools. In addition, it seems that the p.Gly30= (HBD: c.90C>T) decreases the use of authentic splice and, instead, creates a new donor splice site (DSS) or leads to the use of a cryptic DSS.

Conclusions

Most of these variants have been associated with a decrease in Hb A2 levels. Due to the high mutational diversity in the HBB gene in the Iranian population and the use of Hb A2 quantification to differentiate α- and ß-thal carriers among Iranian clinical laboratories, some attention should be taken to a possible co-inheritance of HBD gene variants to avoid the misdiagnosis of ß-thal carriers.

Genetic epidemiology of hemoglobinopathies among Iraqi Kurds

Hemoglobinopathies are major health problems among Iraqi Kurds, who are a distinct ethnic group inhabiting North and Northeastern Iraq. We reviewed published literature on these disorders in this part of the world, and it was revealed that the most prevalent is β-thalassemia with carrier rates of 3.7-6.9%. Alpha thalassemia is less prevalent with carrier rates of 0.03-1.22%, while the sickle cell gene is variably distributed with carrier rates of 0.06-1.2%. Other structural hemoglobinopathies and δβ-thalassemia are sporadic. Twenty-seven different β-thalassemia mutations were identified, with seven constituting 82% of 1039 chromosomes characterized, namely: IVS-II-1 (G>A), IVS-I-6 (T>C), IVS-I-I (G>A), codon 8 (-AA), codon 8/9 (+G), IVS-I-110 (G>A), and codon 5 (-CT). There were notable regional variations in the distribution of β-thalassemia mutations, with Cd44 being mainly prevalent in the North, while IVS-I-110 is mainly prevalent in the East. In relevance to α-thalassemia, ten different mutations were detected, with the four most frequent constituting 92.4% of 262 alleles characterized being: -α^3.7, --^MED, α^-5ntα, and α^PolyA1α. In relevance to sickle cell gene, it is seen in the northern part of the region bordering Turkey, with comparable prevalence rates, and is associated, similar to Turkey, mainly with the Benin haplotype, unlike that in Southern Iraq where it is associated with the Arab-Indian haplotype, similar to Eastern Arabian Peninsula. Given the high prevalence of hemoglobinopathies in the region, and the high rates of consanguineous marriages, a preventive program was initiated in 2008, and results of its first 5 years were promising, though there are still many outstanding challenges that require addressing.

Molecular Genetic Analysis of α-Thalassemia in Hamadan Province, West Iran

Identifying couples who are carriers of thalassemia-causing mutations, followed by prenatal diagnosis (PND), is undoubtedly an effective way to prevent the birth of children with the disease. Our aim in this study was to report for the first time the spectrum of α-globin gene mutations in the population living in Hamadan Province, West Iran. Multiplex gap-polymerase chain reaction (gap-PCR), amplification refractory mutation system (ARMS)-PCR, and direct DNA sequencing of HBA1 and HBA2 genes were used to identify the α-thalassemia (α-thal)-causing mutations in a cohort of 389 individuals including 328 α-thal carriers and 61 normal subjects. A total of 17 different mutations and 25 different genotypes were detected. The -α^3.7 (rightward) deletion (NG_000006.1: g.34164_37967del3804) was the most frequent mutation, accounting for more than half of all mutations (61.04%). This study revealed that there is a variety of α-thal mutations and α-thal genotypes in Hamadan Province, West Iran. This observation is probably due to the complexity of the Hamadan Province population that is composed of Persians (Fars), Turks, Kurds, and Lurs/Laks. In conclusion, our results demonstrated the spectrum of mutations in α-globin genes in Iran and increased our understanding of their distribution in this country.