Sickle cell and thalassaemic genes in Libya

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.

Prevalence of Sickle Cell Trait in the Southern Suburb of Beirut, Lebanon

Objective

The objective of this study was to assess the prevalence, gender differences, and time trends of Sickle Cell Trait in the Southern Suburb of Beirut, Lebanon, as well as to highlight the importance of screening for Sickle Cell Trait carriers in this population. Another objective was to describe a new screening technique for Sickle Cell Trait carriers.

Methods

This was a retrospective cohort study carried out at a private laboratory in the Southern Suburb of Beirut, Lebanon between 2002 and 2014. The sickling test was carried out for each patient using two methods: the classical “sodium metabisulfite sickling test”, and the new “sickling test method” used in the private lab. As a confirmatory test, hemoglobin electrophoresis was run on a random sample of 223 cases which were found to be positive using the two sickling tests.

Results

A total of 899 cases were found to be positive for the sickle cell trait out of 184,105 subjects screened during the 12-year period, prevalence = 0.49% (95% CI: 0.46 – 0.52). Among the total sample, females were found to have higher prevalence, where no time trend over the studied period was noted. The haemoglobin electrophoresis method confirmed the results of this new sickling test technique among the random sample of the 223 cases.

Conclusion

We found that the prevalence of sickle cell trait is lower as compared to other Arab countries, higher in females, with no significant time trend. The sickle cell test was found to be an accurate, simple and cheap test that could be easily added as a requirement for the pre-marital testing to screen for Sickle Cell Trait carriers.

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.

Sickle cell disease in Middle East Arab countries

The sickle cell (HbS) gene occurs at a variable frequency in the Middle Eastern Arab countries, with characteristic distribution patterns and representing an overall picture of blood genetic disorders in the region. The origin of the gene has been debated, but studies using β-globin gene haplotypes have ascertained that there were multiple origins for HbS. In some regions the HbS gene is common and exhibits polymorphism, while the reverse is true in others. A common causative factor for the high prevalence and maintenance of HbS and thalassaemia genes is malaria endemicity. The HbS gene also co-exists with other haemoglobin variants and thalassaemia genes and the resulting clinical state is referred to as sickle cell disease (SCD). In the Middle Eastern Arab countries, the clinical picture of SCD expresses two distinct forms, the benign and the severe forms, which are related to two distinct β-globin gene haplotypes. These are referred to as the Saudi-Indian and the Benin haplotypes, respectively. In a majority of the Middle Eastern Arab countries the HbS is linked to the Saudi-Indian haplotype, while in others it is linked to the Benin haplotype. This review outlines the frequency, distribution, clinical feature, management and prevention as well as gene interactions of the HbS genes with other haemoglobin disorders in the Middle Eastern Arab countries.

Evolution of hemoglobinopathy prevention in Africa: results, problems and prospect

Hemoglobinopathies are a group of inherited hemoglobin disorders. Initially described in the subtropical regions, they are now spread all around the world because of migration. Their high frequency and clinical severity make them a major public health problem mostly in Africa due to the limited resources reserved for the management and prevention of these diseases. Despite considerable advances in the control and management of the hemoglobinopathies, therapeutic approach and follow- up still pose problems because of the major economic and organizational difficulties in the developing countries, particularly in Africa where problems are majored by other factors including social and cultural backgrounds, high consanguinity, as well as the coexistence of infection and malnutrition. Effective prevention programs have been carried out successfully in many European countries concerned by hemoglobinopathies. They should be extended to African regions where hemoglobin disorders account for more than 70% of total hemoglobinopathies in the world. Prevention should remain the major priority of health services to reduce incidence of hemoglobinopathies in Africa. Hereby we present the Tunisian experience that may reflect globally the profile of the prevention evolution of hemoglobinopathies in North Africa.

Splenomegaly in Arab children with idiopathic thrombocytopenic purpura

Splenomegaly was found in 31 (55%) of 56 Arab children with idiopathic thrombocytopenic purpura. Of those with splenomegaly, 84% had evidence of iron deficiency anemia compared to 48% in those without splenomegaly (P<0.001). There was no significant difference in the prevalence of ss-thalassemia trait or history of preceding viral infection between those with or without splenomegaly. This study demonstrates a much higher prevalence of splenomegaly in Arab children with idiopathic thrombocytopenic purpura, most probably related to associated iron deficiency.

Genetic epidemiology of the beta s gene

The beta s gene arose at least four times in Africa, with three of these mutations expanding through diverse ethnic groups, but limited to definite geographical areas: Atlantic west Africa for the Senegal haplotype linked beta s; central west Africa for the Benin haplotype; and equatorial, eastern and southern Africa for the Bantu haplotype. The fourth mutation (linked to the Cameroon haplotype) is restricted to a single ethnic group, the Eton of central Cameroon. The Benin haplotype linked beta s gene was spread by gene flow to the Mediterranean (north, south and east) and to the western portions of Saudi Arabia. An independent mutation linked to a fifth haplotype, Arab-India, is found among the tribals of India (independent from their geographical origin) and in the eastern oases of Saudi Arabia. It is also suspected of being associated with the beta s gene found in Afghanistan, Iran, Transcaucasia and central Asia. The selective force involved in the expansion of the gene was most likely P. falciparum malaria, and the time of the gene frequency increase was likely to have been during the expansion of agriculture about 4000 or more years ago in India and about 3000 years ago in Africa. The partial protection against severe and life-threatening malaria is through the limitation of P. falciparum parasitaemia. This is a complex process which involves at least two mechanisms: early intraerythrocyte parasite forms are in a suicidal position through increasing the tendency of HbAS cell to sickle and then be destroyed by the spleen; intraerythrocyte growth is inhibited during deep vascular schizogony. Although there is evidence that P. falciparum (and P. malariae) parasitaemias are limited in HbSS red cells, malaria is a major trigger to haemolytic and infarctive crises in sickle-cell disease, and a common cause of morbidity and mortality.