Screening of Iranian thalassemic families for the most common deletions of the beta-globin gene cluster

The Spectrum of HBB Mutations among 2315 Beta Thalassemia Patients of a Reference Clinic in Tehran-Iran

Beta Thalassemia is the most prevalent and well-studied single gene disorder in Iran. Here, we investigated the spectrum of HBB gene mutations, identified among 2315 patients, referred to a reference thalassemia clinic in Tehran, on the basis of suspicion to thalassemia major or intermedia. The patients were homozygous or compound heterozygous for HBB mutations, and were referred from various Iranian provinces, during 15 years (2001- 2016). The HBB mutations were classified based on their frequency, and the result was compared to a meta-analysis of 14,293 beta thalassemia cases in the Iranian population, within the same time period. The mutation spectrum in this study contained 43 HBB mutations, compared to the 90, presented by the meta-analysis. Similar to the meta-analysis, IVSII-1 (G > A) and IVSI-5 (G > C) were the most common mutations in this study. These two comprised 62.40% of the total HBB mutant alleles in the studied population, comparable to 51.92% of that in the meta-analysis. IVSII-1 (G > A) and IVSI-5 (G > C), followed by 17 other mutations that had frequencies ranging from 0.15% to 5.44%, were among the 20 common HBB mutations in Iran and neighboring countries, according to the meta-analysis. This study provided further evidence to support the spectrum of the most common HBB mutations in the Iranian population.

Rare and New Mutations of B-Globin in Azari Population of Iran, a Considerable Diversity

Background

Thalassemia, as the most common single-gene genetic disorder, is related to a defect in the synthesis of one or more hemoglobin chains. More than 200 mutations have been identified in the β-globin gene. Globally, every susceptible racial group has its own specific spectrum of the common mutations that are well-known to a particular geographic region. On the other hand, varying numbers of diverse rare mutations may occur.

Materials and Methods

The subjects of the study included 2113 heterozygote or homozygote β-thalassemia cases selected among couples who participated in the Iranian national thalassemia screening program from January 2011 to November 2019. Molecular characterization of the β-thalassemia mutation was initially carried out by the amplification-refractory mutation system-polymerase chain reaction (ARMS-PCR) technique for common mutations, followed by sequencing, Gap PCR, and Multiple ligation-dependent probe amplification (MLPA) methods - in cases not detected by the ARMS-PCR.

Results

The existence of 39 rare and new point mutations and 4 large deletions were described in our cohort. Sicilian (-13,337bp) deletion, CD36/37 (-T), and CD15 TGG>TGA were encountered more often than the others in a decreasing order, in terms of frequency. The least frequent mutations/deletions were deletion from HBD exon 1 to HBB promoter, 619 bp deletion, Deletion from up HBBP1-Exon3 HBBP1 and up HBB-0.5Kb down HBB, CAP+8 C>A, CD37 (G>A), CD6 (-A), IVSI-2 (T>C), IVSII-705 T>G, and IVSII-772 (G>A). Each occurred once. Five mutations/variants were also determined which have not been reported previously in Iran.

Conclusion

According to the findings of the study, the Northwestern Iranian population displayed a wide variety of thalassemia allelic distributions. Identification of rare and new mutations in the β-thalassemia in the national population is beneficial for screening programs, genetic counseling, and prenatal diagnosis.

Molecular characterization of delta beta-thalassemia and hereditary persistence of fetal hemoglobin in the Indian population

delta beta-Thalassemia (delta beta-thal) and hereditary persistence of fetal hemoglobin (HPFH) are heterogeneous disorders characterized by elevated levels of Hb F in adult life. The two disorders should not be considered as unambiguously separate entities but rather as a group of disorders with a variety of partially overlapping phenotypes. This study was undertaken to determine the hematological and molecular characteristics of high Hb F determinants among Indians. A gap-polymerase chain reaction (gap-PCR)-based approach was used for molecular characterization of high Hb F phenotypes. Fifty-five unrelated individuals were studied. The molecular findings were correlated with the hematological data. DNA analysis identified the deletion-inversion (G)gamma((A)gamma delta beta)(0)-thal in 15 cases (27%) and the HPFH-3 (Indian deletion) determinant in 26 cases (47.2%) and the Vietnamese/Chinese determinant (27 kb deletion) in five cases (9%), which is being reported for the first time from India; 16% (nine cases) of the samples remained uncharacterized. This study emphasizes that delta beta-thal and HPFH determinants are common in India. Molecular analysis will aid in understanding genotype-phenotype correlations and will facilitate prevention and control programs of thalassemia and hemoglobinopathies in this region.