Molecular heterogeneity of beta-thalassemia in Algeria: how to face up to a major health problem

Global distribution of β-thalassemia mutations: An update

One excellent illustration of how a single gene abnormality may result in a spectrum of disease incidence is the incredible phenotypic variety of β-thalassemia, which spans from severe anemia and transfusion needs to an utterly asymptomatic sickness. However, genetic causes of β-thalassemia and how the anemia's severity might be altered at various stages in its pathophysiology have been well investigated. There are currently known to be more than 350 mutations that cause genetic disease. However only 20 β thalassemia mutations account for more than 80% of the β thalassemia mutation across the globe due to phenomenon of geographical clustering where each population has a few common mutations together with a varying number of rare ones. Due to migration of the population, the spectrum of thalassemia mutation in changing from time to time. In this review, efforts are made to collate β globin gene mutations in different countries and populations.

Molecular heterogeneity of β-thalassemia variants in the Eastern region of Morocco

Background

β‐thalassemia syndromes are the most common hereditary blood disorders in the world and are recognized as a major health problem in Morocco. They are characterized by the reduction or the absence of β‐globin chain synthesis. The severity of the disease depends on the nature of the variants affecting the β‐globin gene (HBB), and each ethnic group has its own mutation spectrum. Hereby, we present, for the first time, the molecular profile of β‐thalassemia in the Eastern region of Morocco.

Methods

This study concerns 39 cases from 33 families who were enrolled in the BRO Biobank. Nineteen were diagnosed with β‐thalassemia major and 20 with β‐thalassemia minor. To detect mutations of the β‐globin gene, we have used RFLP‐PCR and Sanger sequencing.

Results

Nine known β‐thalassemia variants have been identified. Among these, we reported, for the first time in the Moroccan population, the Czechoslovakian variant C38/39(‐C) at homozygous state. The C39(C > T) was the most frequent variant (72.54%), followed by FSC5(‐CT) (5.88%), FSC6(−A), IVS‐1‐110(G > A), −29(A > G), C38/39(‐C) (3.92% each), and finally by IVS‐I‐1(G > A), IVS‐II‐1(G > A), and −56(G > C) (1.96%). Of particular interest this mutational spectrum of β‐thalassemia is very different from that found in previous studies in Morocco or in other North African countries.

Conclusion

This study is the first contribution to the description of the molecular profile of β‐thalassemia in the Eastern region of Morocco. It shows the high molecular heterogeneity of β‐thalassemia in our country. Therefore, these results can be valuable for the implementation of carrier screening, genetic counseling, and prenatal diagnosis programs.

The spectrum of beta-thalassemia mutations in the 22 Arab countries: a systematic review

OBJECTIVES

To investigate the mutational spectrum in the HBB gene in Arab patients with β-thal.

METHODS

Authors searched five databases (PubMed, Science Direct, Scopus, Web of Science, and Google Scholar) from the time of inception until March 2020.

RESULTS

The authors search strategy yielded 3,229 citations, of which 48 eligible studies captured. 105 mutations were captured, of these, 99 were shared between Arabs and other ethnic groups, six mutations were unique to Arabs (c.92 + 2 T > G, c.-240 G > A, c.150delC, c.420dupT, deletion of 192 bp spanning exon 1, intron 1, and the first two bases of exon 2 of HBB gene, and deletion of 9.6 kb, including exon 1 and intron 2 of HBB gene). The most common HBB gene mutations among Arabs were c.93-21 G > A, c.118 C > T, c.92 + 1 G > A, c.92 + 6 T > C, c.92 + 5 G > C, c.315 + 1 G > A, and c.27dupG. Consanguinity is high among Arab patients with β-thal. Migration into Arab countries led to allelic heterogeneity among Arab patients with β-thal.

CONCLUSION

Our findings present a platform for further genetic epidemiological studies for Arab patients with β-thal.

Consanguinity and Inbreeding in Health and Disease in North African Populations

North Africa is defined as the geographical region separated from the rest of the continent by the Sahara and from Europe by the Mediterranean Sea. The main demographic features of North African populations are their familial structure and high rates of familial and geographic endogamy, which have a proven impact on health, particularly the occurrence of genetic diseases, with a greater effect on the frequency and spectrum of the rarest forms of autosomal recessive genetic diseases. More than 500 different genetic diseases have been reported in this region, most of which are autosomal recessive. During the last few decades, there has been great interest in the molecular investigation of large consanguineous North African families. The development of local capacities has brought a substantial improvement in the molecular characterization of these diseases, but the genetic bases of half of them remain unknown. Diseases of known molecular etiology are characterized by their genetic and mutational heterogeneity, although some founder mutations are encountered relatively frequently. Some founder mutations are specific to a single country or a specific ethnic or geographic group, and others are shared by all North African countries or worldwide. The impact of consanguinity on common multifactorial diseases is less evident.

Presence of the IVS-I-6-Mutated Allele in Beta-Thalassemia Major Patients Correlates with Extramedullary Hematopoiesis Incidence

Extramedullary hematopoiesis (EMH) results from the extension of hematopoietic tissue beyond the confines of the bones. Since the initiation of regular transfusion programs from an early age for all thalassemia major (ΤΜ) patients, EMH has not been considered a clinical issue anymore. The present study aims to record the prevalence of EMH in chronically transfused ΤΜ patients followed at our institution and to investigate possible risk factors associated with its occurrence. The project was designed as a retrospective, nonexperimental, descriptive, exploratory study. In total, the study enrolled 104 patients. EMH was revealed in 15/104 (14%) patients. The presence of intravening sequence (IVS)-I-6 was significantly related with the development of EMH (p < 0.05). No other demographic or biological factor studied was found to be related with the presence of EMH. The study stresses a profound incidence of asymptomatic EMH in a solid group of well-transfused ΤΜ patients. Given the high incidence of the IVS-I-6 allele in the Mediterranean and Middle Eastern region, high-quality, prospective, multicenter studies could confirm the association of EMH occurrence with the presence of the IVS-I-6 mutation and further evaluate the exact role of this mutation in the EMH process.

Two new β+ -thalassemia mutation [β -56 (G → C); HBBc. -106 G → C] and [β -83 (G → A); HBBc. -133 G → A] described among the Tunisian population

OBJECTIVES

Different thalassemia mutations have been reported in various ethnic groups and geographical regions in Tunisia. In the present study, we have investigated two rare β(+) -thalassemia mutations, that have not previously been reported in the Tunisian population [β -56 (G > C); HBBc. -106 G > C] and [β -83 (G > A); HBBc. -133 G > A].

METHODS

The whole β-globin gene was directly sequenced, and haplotype analysis was conducted through a PCR/RFLP method.

RESULTS

Two new mutations were identified for the first time in Tunisia. They are located within the promoter region of β-globin gene at position -56 (G > C) and -83 (G > A). Linkage analysis using β-globin gene cluster haplotypes showed that these two mutations were associated with Mediterranean β-haplotype IX [- + - + + + +] and framework 2 (FW2) [CCTCT].

CONCLUSIONS

The two newly described mutations lead to the β(+) -thalassemia among Tunisian patients. The haplotype analysis and framework assignment have helped to identify the chromosomal background associated with these mutations, and determine their origin and spread.

Prevalence of β-Thalassemia and hemoglobin E in two migrant populations of Manipur, North East India

Hemoglobinopathies are a group of inherited single-gene disorders found commonly in the Mediterranean region, Middle East, Indian subcontinent, Burma, and South East Asia. As many as 229 mutation variants of β-thalassemia are reported in the world, many community/region-specific mutations. Very little on thalassemia has been reported in Manipur, a North Eastern Indian state. Thus, a community genetic approach through population screening can be applied to the people of Manipur and a total of 602 blood samples from unrelated Meitei Brahmins (n=300) and Meitei Muslims (n=302) were screened for abnormal hemoglobins by Naked Eye Single Tube Red Cell Osmotic Fragility Test (NESTROFT). HBA(2) level was estimated by using high-performance liquid chromatography and molecular analysis was done by using PCR. Sequencing was also carried out to confirm the mutations. High frequencies of NESTROFT positive (10%) and NESTROFT doubtful (11%) cases were found among the Meitei Brahmins in comparison to the Meitei Muslims [NESTROFT positive (3.31%) and NESTROFT doubtful (1.33%)]. The allele frequency of HB*E was 0.022 and 0.012 among the Meitei Brahmin and Meitei Muslim, respectively. Sequencing of the β-globin gene confirmed a very rare β-thalassemia [-90 C→T (0.33%)] among the Meitei Brahmins of Manipur. This mutation with hemoglobin E in one of the present population hints the presence of the Mongoloid stock among them, possibly from China. There is a need for further studies on other populations of Manipur and the neighboring North East Indian states using such genetic markers.

Epidemiological profile of common haemoglobinopathies in Arab countries

Haemoglobinopathies including the thalassemias and sickle cell disease are known to be prevalent inherited disorders in most Arab countries with varying prevalence rates and molecular characterisation. β-thalassemia is encountered in polymorphic frequencies in almost all Arab countries with carrier rates of 1-11 % and a varying number of mutations. The most widespread mutation in Lebanon, Egypt, Syria, Jordan, Tunisia and Algeria is the IVS-I-110 (G>A). In the Eastern Arabian Peninsula, the Asian Indian mutations (IVS-I-5 (G>C), codons 8/9 (+G) and IVS-I (-25 bp del)) are more common. The α-thalassemias are encountered in the majority of Arab countries in frequencies ranging from 1 to 58 % with the highest frequencies reported from Gulf countries. The (-α(3.7)) mutation is the most frequent followed by the non-deletional α2 polyadenylation signal mutation (AATAAA>AATAAG) and the α2 IVS1 5-bp deletion. The rates of sickle cell trait in Arab countries range from 0.3 to 30 %, with the Benin, the Arab-Indian and the Bantu haplotypes constituting the bulk of the haplotypes, leading to two major phenotypes; a mild one associated with the Arab-Indian and a severe one with the Benin and Bantu haplotypes. Public health approaches targeting prevention of haemoglobinopathies in Arab countries include newborn screening for sickle cell disease, and premarital screening for carriers of β-thalassemia and sickle cell disease. These services are still patchy and inadequate in many Arab countries recommending the upgrade of these services with strengthening of the education and training of health care providers and raising public awareness on the feasibility of prevention and care for haemoglobinopathies.