Molecular Basis of α-Thalassemia in Algeria

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.

α-Globin Genotypes Associated with Hb H Disease: A Report from Oman and a Review of the Literature from the Eastern Mediterranean Region

α-Thalassemia (α-thal) is the most common autosomal recessive hemoglobinopathy. There is a vast diversity and geographical variability in underlying genotypes in Hb H (β4) patients. Herein, we describe the genotypes found in the largest report of Omani Hb H patients. Moreover, we reviewed and summarized the literature published from the Eastern Mediterranean region. A retrospective review of all genetically confirmed Hb H disease patients diagnosed between 2007 and 2017 at Sultan Qaboos University Hospital, Muscat, Oman, was performed. Hematological parameters and clinical presentations were assessed. Both α-globin genes were screened for deletional and nondeletional mutations using a stepwise diagnostic strategy as described before. A total of 52 patients (27 females and 25 males) with a mean age of 20.6 years (range 0.23-80.0) were molecularly confirmed to carry Hb H disease. The patients had a hemoglobin (Hb) level of 9.3 g/dL (range 5.7-13.0) and mean corpuscular volume (MCV) of 58.4 fL (range 48.2-82.1). A total of eight genotype combinations were identified, with α2 polyadenylation signal mutation (polyA1) (AATAAA>AATAAG (α^PA1α/α^PA1α), often cited as α^T-Saudiα/α^T-Saudiα, being the most common (53.8%) followed by -α^3.7/- -^{MED I} (28.8%). Our cohort also included patients with combinations of α^PA1 with other Hb variants: α^PA1α/α^PA1α with Hb S (HBB: c.20A>T) trait (n = 2), -α^3.7/α^PA1α (n = 2) and α^{codon 19}α (HBA2: c.56delG)/α^PA1α (n = 1). Nondeletional Hb H disease due to the α^PA1 mutation is the most common in Omanis. Molecular diagnosis is necessary for accurate confirmation of the diagnosis of α-thal, determination of underlying genotypes, follow-up and counseling.

Diagnosis and Prenatal Diagnosis in a Chinese Family Carrying the Rare α-Thalassemia Gene HBA2: c.1A>G Mutation

The aim of this study was to identify the rare thalassemia genotype in a family and perform prenatal diagnosis (PND) on the proband's unborn child. Peripheral blood was collected from the family members for hematology analysis and capillary electrophoresis (CE) analysis. Peripheral blood and cord blood were analyzed by gap-polymerase chain reaction (gap-PCR), reverse dot-blot and Sanger sequencing for genotypes of α-thalassemia (α-thal). A heterozygous mutation, HBA2: c.1A>G, was identified in the proband and his father. Two compound heterozygous variants, HBA2: c.1A>G and the - -^SEA (Southeast Asian) deletion, were revealed in the proband's unborn child. The hemoglobin (Hb) CE result of the fetal cord blood indicated the fetus had Hb H disease. We have identified a rare thalassemia mutation (HBA2: c.1A>G) in a Chinese family and enriched the rare α-thal gene pool in the Chinese population. When the patient's phenotype does not match the genotype detected by thalassemia gene detection kits, further investigation of rare genotypes should be conducted to avoid missed diagnosis or misdiagnosis, which can help guide clinical diagnosis, population screening and genetic counseling.

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.

Alpha-Thalassemia in North Morocco: Prevalence and Molecular Spectrum

Unlike the other hemoglobinopathies, few researches have been published concerning α-thalassemia in Morocco. The epidemiological features and the mutation spectrum of this disease are still unknown. This regional newborn screening is the first to study α-thalassemia in the north of Morocco. During the period from January 2015 to December 2016, 1658 newborns umbilical blood samples were investigated. Suspected newborns were screened for α-globin defects using Gap-PCR and Multiplex Ligation-dependent Probe Amplification technique. The prevalence of α-thalassemia, its mutation spectrum, and its allelic frequencies were described for the first time in Morocco. Six different α-globin genetic disorders were detected in 16 neonates. This screening valued the prevalence of α-thalassemia in the studied population at 0.96% and showed the wide mutation spectrum and the heterogeneous geographical distribution of the disease. A high rate of carriers was observed in Laouamra, a rural commune in Larache province. Heterogeneity of α-globin alleles in Morocco explains the high variability of α-thalassemia severity. This diversity reflects the anthropological history of the country. These results would contribute to the prevention of thalassemia in Morocco directing the design of a nationwide screening strategy and awareness campaign.

A Comprehensive Molecular Investigation of α-Thalassemia in an Iranian Cohort from Different Provinces of North Iran

α-Thalassemia (α-thal) is the most common monogenic disease that is caused by the absence or reduced expression of α-globin genes. The aim of this study was to investigate common α-globin mutations and their associated haplotypes in four northern provinces of Iran (Gilan, Mazandaran, Golestan, Khorasan). One thousand, one hundred and ninety-one persons were tested for α-thal mutations by gap-polymerase chain reaction (PCR), reverse dot-blot hybridization, restriction fragment length polymorphism (RFLP) analysis and sequencing. Of the nine different mutations found, the most frequent were -α^3.7 (rightward deletion) (45.6%), polyadenylation site (α^p°^lyA2α) (α2) (AATAAA>AATGAA; HBA2: c.*92 A>G) (15.27%), - -^MED (Mediterranean deletion) (6.86%), -α^4.2 (leftward deletion), (6.17%), α^CSα [Hb Constant Spring (Hb CS) (HBA2: c.427 T>C)] (4.62%), -α^-5 nt (HBA2: c.95+2_95+6delTGAGG) (3.70%). All chromosomes bearing an α-globin point mutation [α^p°^lyA2α, -α^-5 ntα, α^CSα, α^p°^lyA1α (AATAAA> AATAAG; HBA2: c.*94 A>G)] showed only one haplotype that was present in most normal chromosomes, while the -α^3.7 deletion was associated with three distinct haplotypes. Our results indicate that α-thal mutations are heterogeneous and -α^3.7 and α^p°^lyA2α are the most prevalent mutations in this region. The presence of -α^3.7 with three different haplotypes suggests an older history for this mutation. The high prevalence of α^p°^lyA2α in Mazandaran Province, Iran compared to other parts of the country and the world, suggests a founder effect. Altogether, we here provide further data confirming the heterogeneity of the northern population of Iran. These data may contribute to the establishment of a national mutation database, more accurate genetic counseling and prenatal diagnosis (PND).

Incidence of alpha-globin gene defect in the Lebanese population: a pilot study

Background. It is well established that the Mediterranean and Arab populations are at high risk for thalassemias in general and for alpha-thalassemia in particular. Yet, reports on alpha-thalassemia in Lebanon are still lacking. In this study, we aim at assessing the incidence of alpha-thalassemia in the Lebanese population. Methods. 230 newborns' dried blood cards remaining from routine neonatal screening at the American University of Beirut Medical Center were collected for DNA extraction. Samples were screened for the 21 most common α-globin deletions and point mutations reported worldwide, through multiplex Polymerase Chain Reaction (PCR) and Reverse-Hybridization technique. Results. Upon analyses, the carrier rate of α-thalassemia was found to be 8%. Two mutations detected the −α^3,7 single gene deletion found in 75% of cases and the nongene deletion α2 IVS1 [−5nt] in the remaining samples. Conclusion. This study is the first dedicated to investigate α-thalassemia trait incidence in Lebanon. Data obtained demonstrates a high carrier rate in a relatively, highly consanguineous population; it also highlighted the presence of two common mutations. These results may be of an important impact on premarital and newborn screening policies in our country.

Alpha thalassemia allelic frequency in Lebanon

BACKGROUND

Hemoglobinopathies are the most common reported monogenic disorders worldwide. It is well established that Mediterranean and Arab countries are high risk areas for thalassemia in general, and for alpha thalassemia in particular. Reports of alpha thalassemia gene mutations from the Lebanese population are limited.

PROCEDURE

We investigated the spectrum of alpha thalassemia mutations in a sample of 70 unrelated Lebanese families. Six different mutations of alpha thalassemia gene were identified.

RESULTS

The most prevalent mutations were the single gene deletion -α(3.7) (43%) and the non-gene deletion α2 IVS1 [-5nt] (37%). The double deletional determinant -(MED) was detected only in 14% of thalassemic chromosomes.

CONCLUSION

We determined the mutational spectrum of alpha thalassemia which might be used in the future for molecular investigations of the disease in susceptible patients in our population.

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 spectrum of α-thalassemia mutations in the Kurdish population of Northeastern Iraq

In an attempt to determine the spectrum of α-thalassemia (α-thal) mutations in the Kurdish population of Northeastern (NE) Iraq, a total of 101 unrelated adults with unexplained hypochromia and/or microcytosis were enrolled. α-Thalasssemia mutations were characterized by gap polymerase chain reaction (gap-PCR), multiplex PCR (m-PCR) and reverse hybridization and sequencing for both α genes. A total of nine α-thal mutations were characterized including four deletional ones: -α(3.7) (rightward), - -(MED-I), -(α)(20.5), -α(4.2) (leftward) and five nondeletional ones: α(polyA1)α, αα(Adana), α(-5 nt)α, α(CS)α and α(polyA2)α. These determinants were arranged in 12 different genotypes, the most frequent of which were: -α(3.7)/αα, - -(MED-I)/αα, -α(3.7)/-α(3.7), α(polyA1)α/αα, αα(Adana)/αα and -(α)(20.5)/αα. This pattern is similar to that reported in Turkey, western (W) Iran, Cyprus and Greece, and to some extent, different from the pattern observed in the Arabian Peninsula.