Beta-thalassemia in Algeria

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.

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.

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.

The significance of the hemoglobin A(2) value in screening for hemoglobinopathies

BACKGROUND AND OBJECTIVE

The inherited hemoglobinopathies are a large group of disorders that include thalassemias and hemoglobin variants. Accurate determination of the carrier phenotype is essential for detecting couples at risk for producing offspring with hemoglobinopathy. Heterozygous beta-thalassemia is usually silent at the clinical level. His phenotype is characterized by microcytosis and hypochromia with increased hemoglobin A(2) (HbA(2)) value. Therefore, HbA(2) determination plays a key role in screening programs for hemoglobinopathy. The aim of this review is to address and suggest an approach for reducing or abolishing hemoglobinopathy screening mistakes.

DESIGN AND METHODS

Quantitative methods for HbA(2) value determination, comment on the accuracy of the test and on the interpretation of data were discussed. The most probable diagnostic conclusion based on the HbA(2) level, hemoglobin pattern, hematological parameters and iron markers was suggested in this review.

RESULTS

Hemoglobinopathies are the only genetic disease where it is possible to detect carriers using hematological findings rather than DNA analysis. However, hematological diagnosis is sometimes presumptive, and in these cases, DNA analysis becomes necessary. Complete screening is based on the detection of red cell indices, HbA(2), HbF and hemoglobin variant values. In particular, HbA(2) determination plays a key role in screening programs for beta-thalassemia because a small increase in this fraction is one of the most important markers of beta-thalassemia heterozygous carriers.

CONCLUSION

Genetic factors both related and unrelated to the beta- and alpha-globin gene clusters, iron metabolism, endocrinological disorders, and some types of anemia, together with intra- and inter-laboratory variations in HbA(2) determination, may cause difficulties in evaluating this measurement in screening programs for hemoglobinopathies. Therefore, knowledge of all these issues is important for reducing or eliminating the risk of mistakes in screening programs for hemoglobinopathies.

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

This study concerns the molecular characterization of beta-thalassemia (beta-thal) alleles in 210 chromosomes. In the studied population, mutations were detected in 98% of the beta-thalassemic chromosomes. Twenty-one molecular defects have been found, where the five dominant mutations, IVS-I-110 (G>A), nonsense mutation at codon 39 (C>T), the frameshift codon (FSC) 6 (-A), IVS-I-1 (G>A), and IVS-I-6 (T>C), account for 80% of the independent chromosomes. Among the remaining alleles, 16 different mutations were identified, half of them being described for the first time in Algeria. These include the -101 (C>T) and the -90 (C>T) mutations in the distal and proximal promoter elements, respectively, the FSC 8 (-AA), IVS-I-5 (G>T), IVS-I-128 (T>G), FSC 47 (+A), IVS-II-1 (G>A), and the substitution in the polyadenylation signal (poly A) site AATAAA>AATGAA. Haplotype analyses on rare variants were performed. The possible origin of these mutations either by founder effect or by migrations is discussed, and raises the question of an adequate strategy to be used adapted to socio-economical status.

Genotypic correlation between six common beta-thalassemia mutations and the XmnI polymorphism in the Moroccan population

beta-Thalassemia (thal) is the most common recessive inherited disorder in Mediterranean populations. It is estimated that the frequency of this disease in the Moroccan population is between 1.5 and 3.0%. Severe forms of homozygous thalassemia cases require expensive and technically demanding curative (bone marrow transplantation) or palliative (chronic transfusion/chelation) therapies. The -158 (C-->T) polymorphism of the (G)gamma-globin gene (XmnI polymorphism) is known to ameliorate the severity of the disease because of it strong association with an increased production of fetal hemoglobin (Hb F). Among the many known mutations in Morocco, six are common [codon 39 (C-->T), frameshift codon (FSC) 8 (-AA), IVS-II-745 (CG), FSC 6 (-A), -29 (A-->G) and IVS-I-1 (G-->A)]. In this study, we have investigated, in 82 Moroccan beta-thalassemic chromosomes, the correlation between the six common mutations and the XmnI polymorphism using the Fisher exact test. The XmnI polymorphism was divided into two categories, (XmnI [+] and XmnI [-]) and the six common Moroccan mutations into two groups (group I with FSC 8 and group II without FSC 8). Correlation was carried out between the XmnI [+] category and the six common mutations individually that showed that 68% of chromosomes in the XmnI [+] category had the FSC 8 (-AA) mutation. The results reported here show that there is a positive correlation between the XmnI polymorphism and FSC 8 mutation in linkage with haplotype IV [- + - + + - +] (p <10(-5)). In conclusion, molecular determination of genetic markers in early childhood will help to identify candidates for pharmacological Hb F switching by hydroxyurea (HU). In the Moroccan population, a good response to HU treatment should be suspected in cases with the -158 (C-->T) polymorphism in linkage with haplotype IV and internal beta-globin gene framework 3.

Clinical and molecular aspects of haemoglobinopathies in Tunisia

BACKGROUND

For the last two decades, studies on the population genetics of Tunisians have focused on variations of protein and genetic markers. Results confirmed the genetic heterogeneity of Tunisians caused by the admixtures with migratory human groups arriving mainly from Africa, Europe, and Asia. These studies also allowed the screening of rare mutants and many haemoglobin variants.

METHODS

The present study delineates the incidence of the different haemoglobinopathies in Tunisia. Previously collected data and results obtained from epidemiological and clinical studies of 1238 blood donors and 276 patients were compared. The chromosomal backgrounds of different haemoglobinopathies were explored by molecular techniques (denaturing gradient gel electrophoresis (DGGE), amplification refractory mutation system (ARMS) polymerase chain reaction (PCR), and sequencing).

RESULTS

This study indicates that appropriate DNA methodologies required for a nationwide preventive program in Tunisia are available and that prenatal diagnosis is feasible. Additionally, analysis of sequence polymorphisms allowed a better understanding of the gene recombination events and their application for tracing back the origin and the diffusion of the mutations.

CONCLUSIONS

Molecular analysis techniques such as DGGE and ARMS PCR are socially and economically the most suitable techniques to be used in Tunisia for the detection and the identification of haemoglobin abnormalities. At present, their use is essential to conduct a clear and efficient screening program.

Spectrum of beta-thalassemia in Jordan: identification of two novel mutations

Two hundred and forty-four beta-thalassemia alleles were identified from 135 unrelated occasionally and periodically transfusion dependent beta- and S/beta-thalassemia patients from all regions of Jordan. Allele identification was achieved by PCR amplification of beta-globin genes, dot-blotting the amplified DNA, hybridization with allele specific synthetic probes, and direct sequencing of amplified genomic DNA. A total of 19 different mutations were detected, eight of them constituted about 86% of the Jordanian thalassemic chromosomes. These mutations were IVS1-110 (G>A) (25%), IVS2-1 (G>A) (15%), IVS2-745 (C>G) (14.2%), IVS1-1 (G>A) (10%), IVS1-6 (T>C) (8.3%), codon 37 (G>A) (6.3%), codon 39 (C>T) (4.6%), and codon 5 (-C) (3.8%). The remaining eleven mutations were rare, presented with frequencies ranging between 0.4% and 1.6%. These included two novel mutations and four others detected in Jordan for the first time. The novel mutations were the frame shift (-C) at codon 49 and the substitution (A>C) at position -29 in the TATA box. Four alleles (1.6%) remained unidentified; having no abnormalities in their beta-globin gene sequences and therefore, constituted additional defects causing beta-thalassemia in the Jordanian population. These unknown alleles are expected to be candidates for upstream or downstream mutations affecting the expression of beta-globin gene. The results provided the essential foundation for planning a national preventive program for thalassemia in Jordan and will help improving the medical services for the patients and their families by helping their clinicians and genetic counselors in evaluating their variants and designing their treatment regimens.

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.

Genetic heterogeneity of beta-thalassemia in southeast Sicily

In this study we have defined the spectrum of the beta-thalassemia mutations, the beta-thalassemia haplotypes, and the genotype-to-phenotype correlations in a large number of patients with different beta-thalassemia conditions. Seventeen different beta-thalassemia mutations were detected which included one chromosome each with Hb Dhonburi and Hb Lepore. Five alleles, namely, codon 39 (C-->T), IVS-I-110 (G-->A), IVS-I-6 (T-->C), IVS-II-745 (C-->G), and IVS-I-1 (G-->A), account for 90% of all beta-thalassemia mutations in 846 thalassemic chromosomes studied. Haplotyping for a large number of subjects showed that the five common mutations are linked to a few haplotypes. The presence of milder mutations, mainly IVS-I-6 (T C), in about 19% of our patients explains some of the clinical variables. Among the 37 patients with thalassemia of intermediate severity, only 6 were homozygous or compound heterozygous for two severe alleles. The type of beta-thalassemia is the main factor responsible for differences in the phenotypic expression of the disease in patients with Hb S-beta-thalassemia; patients with Hb S-beta(+)-thalassemia are less severely affected than those with Hb S-beta(0)-thalassemia. The five most frequent mutations have comparable distributions all over Sicily.

Molecular characterization of beta-thalassemia in north Jordan

We have studied the beta-thalassemia mutations in 91 chromosomes of 43 patients with beta-thalassemia major and five with Hb S-beta-thalassemia, aged 6 months to 24 years. Many are blood transfusion-dependent and are being treated at the major hospital, the Princess Basma Hospital, in Irbid, Jordan. As many as 13 different mutations have been identified; three Mediterranean mutations [IVS-I-110 (G-->A), IVS-II-I (G-->A), and IVS-II-745 (C-->G)] were present in 54% of the chromosomes tested, while six other Mediterranean alleles were found in 24% of the chromosomes, for a total of 78% of Mediterranean origin. Sixteen chromosomes carried mutations which were observed in Arabian, Southeast Asian/Indian, and Iranian/Egyptian or Black populations; four beta-thalassemia mutations remained unidentified.

The spectrum of beta-thalassaemia in Algeria: possible origins of the molecular heterogeneity and a tentative diagnostic strategy

We report here on the final results of an epidemiological survey involving 177 beta-thalassaemic chromosomes in Algeria. Four common mutations account for 86% of the chromosomes, the other ones carrying nine other rare mutations. Combination of these results with those of other smaller regional epidemiological studies indicates the existence of still a wider range of mutations. The nature and frequencies of these mutations, their linkage with RFLP-haplotypes, agree well with the history of the region. Knowledge of this spectrum of mutations enables the design of a diagnosis strategy that takes into account the local economical constraints.