Spectrum of beta-thalassemia mutations in Oman

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.

Noninvasive assessment and risk factors of liver fibrosis in patients with thalassemia major using shear wave elastography

OBJECTIVES

This study aimed to estimate the prevalence of liver fibrosis and assess the risk factors for developing significant liver fibrosis in patients with Thalassemia Major (TM).

METHODS

All patients with TM over the age of 10 years were included in the study.

RESULTS

A total of 94 eligible patients underwent 2-D SWE. The median age was 26.7 years. The median of the average 5-year serum ferritin (5yrSF) and liver iron concentration (LIC) assessed by MRI T2* were 1326 µg/L and 6.7 mg/g dw, respectively. Hepatitis C and hepatitis B core antibodies were positive in 38% and 1% of the patients respectively. The proportion of patients with significant fibrosis was 60%. Male gender increased the risk of significant fibrosis (Odds ratio of 0.4; p = .0373). Additionally, the 5yrSF (p = .00661), the LIC (p = .0225) and the lowest LIC of the previous 5 years (p = .0211) were significant. In the multivariable logistic regression model, only 5yrSF (p = .0035) and gender (p = .00984) remained significant.

CONCLUSIONS

The risk of liver fibrosis is associated with iron overload and gender in patients with TM.

Repository of mutations from Oman: The entry point to a national mutation database

The Sultanate of Oman is a rapidly developing Muslim country with well-organized government-funded health care services, and expanding medical genetic facilities. The preservation of tribal structures within the Omani population coupled with geographical isolation has produced unique patterns of rare mutations. In order to provide diagnosticians and researchers with access to an up-to-date resource that will assist them in their daily practice we collated and analyzed all of the Mendelian disease-associated mutations identified in the Omani population. By the 1 (st) of August 2015, the dataset contained 300 mutations detected in over 150 different genes. More than half of the data collected reflect novel genetic variations that were first described in the Omani population, and most disorders with known mutations are inherited in an autosomal recessive fashion. A number of novel Mendelian disease genes have been discovered in Omani nationals, and the corresponding mutations are included here. The current study provides a comprehensive resource of the mutations in the Omani population published in scientific literature or reported through service provision that will be useful for genetic care in Oman and will be a starting point for variation databases as next-generation sequencing technologies are introduced into genetic medicine in Oman.

Broader spectrum of β-thalassemia mutations in Oman: regional distribution and comparison with neighboring countries

The objective of this study was to expand and study the molecular spectrum of β-thalassemia (β-thal) mutations in Oman by examining cases from seven different regions and comparing the prevalence with neighboring countries. A total of 446 cases of β hemoglobinopathies was obtained and analyzed to determine the frequency and distribution of the different β alleles. The molecular spectrum of β-thal in Oman revealed the presence of 32 mutations from different origins and 11 alleles are reported for the first time in the Omani population. The wide heterogeneous spectrum of β-thal mutations found can be associated with the history of trade and migration as well as the past domination from other countries. The presented data will facilitate the development of a comprehensive prevention strategy in Oman.

Genetic services and testing in the Sultanate of Oman. Sultanate of Oman steps into modern genetics

The Sultanate of Oman is a rapidly developing Muslim country with well-organised government-funded health care services, including primary, secondary and tertiary, and rapidly expanding medical genetic facilities. At the present time, the Omani population is characterised by a rapid rate of growth, large family size, consanguineous marriages, and the presence of genetic isolates. The preservation of a tribal structure in the community coupled with traditional isolation has produced unique and favourable circumstances for building genealogical records and the study of genetic disease. Genetic services developed in the Sultanate of Oman in the past decade have become an important component of health care. The recently constructed Genetic Centre in Muscat expects to meet the needs of the Omani population in provision of genetic services and research, in a manner deferential to the cultural and religious traditions of the country.

Sistani population: a different spectrum of β-thalassemia mutations from other ethnic groups of Iran

This study aimed to characterize the molecular spectrum of β-thalassemia (β-thal) mutations and evaluate the services available for prenatal diagnosis (PND) among the Sistani population of Iran. Mutations were analyzed with amplification refractory mutation system (ARMS), gap-polymerase chain reaction (gap-PCR), multiplex ligation-dependent probe amplification (MLPA) analysis and direct sequencing. Fetal diagnosis was also confirmed by linkage analysis. Over a 9-year period (2002-2011), 405 at-risk Sistani couples were referred for mutation analysis and/or PND. Of the referred couples, 18.5% had one to three affected children with β-thal major (β-TM) and the remainder had no children or were not married. Most of the couples (73.3%) lived in urban areas and the rate of consanguineous marriage was 76.8%. Twenty-one mutations were identified, of which the most frequent ones were IVS-I-5 (G>C) with a frequency of 74.1%, followed by codon 15 G>A (5.0%), codon -88 (C>T) (3.8%), IVS-II-1 (G>A) (3.4%), codons 8/9 (+G) (2.9%) and IVS-I-1 (G>T) (2.7%), which accounted for about 91.9% of the total β-thal mutations for this region. Furthermore, fetal DNA was obtained from chorionic villus sampling (CVS) for 266 pregnant women and 68 (25.5%) fetuses were diagnosed as affected. In summary, β-thal mutations are very heterogeneous and significantly different from those found in other parts of Iran and are similar to those of Pakistani and Indian populations. These results could greatly facilitate timely and accurate PND.

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 β-globin promoter -71 C>T mutation is a β+ thalassemic allele

A novel β-globin gene promoter (-71 C>T) nucleotide change was recently posted to the HbVar database (ID 2701) without precision on phenotype and ethnicity. We found the same change in compound heterozygosity with Hb S [β6(A3)Glu>Val] in an Omani family with almost equal expression of Hb A and Hb S. This suggested that the -71 C to T mutation may be a mild β-thalassemic allele. Subsequent search found three other independent cases with the same atypical Hb A:Hb S ratio, further confirming the mild thalassemic feature of this mutation. In addition, molecular screening of a set of subjects (with only Hb A) with borderline Hb A(2) or MCV values revealed the presence of -71 C>T change in heterozygous state, altogether assigning the mutation as a mild β(+) thalassemic allele. In a region such as Oman, where several genetic conditions of the red blood cell coexist (α- and β-thalassemia, Hb S, Hb D, Hb E) in significant frequencies, it is crucial to decipher the molecular basis of these atypical forms of β(+) thalassemias, especially in a genetic counseling setting.

Spectrum of β-thalassemia mutations in the eastern province of Saudi Arabia

β-Thalassemias comprise a group of heterogeneous hemoglobin (Hb) disorders characterized by the absence or reduced synthesis of the β-globin chain with a variable clinical presentation. The Al-Qatif and Al-Ahsa oases in the Eastern Province of Saudi Arabia are regions known for the high prevalence of these disorders. This study was conducted to provide a more precise picture of the β-thalassemia (β-thal) mutations prevalent in these regions and to estimate their frequencies. One hundred and 96 subjects with transfusion-dependent β-thalassemia (β-thal) disease were included in this study. A total of 14 β-thal mutations were identified with five mutations accounting for more than 80% of the total β-thal mutations identified. Of the 196 patients, 164 were homozygous for a β-thal mutation, while 32 were compound heterozygotes. We report here the novel identification of two mutations, namely, the Tunisian splice site IVS-I-130 (G→C) and the Mediterranean cryptic splice site IVS-I-110 (G→A), which have not been previously reported in the population of the Eastern Province. However, 15 patients (46.9%) with compound heterozygosities carried one of the β-thal mutations and the sickle cell mutation [Hb S or β6(A3)Glu→Val]. These patients were less frequently transfused than the patients who were homozygous for the β-thal mutations and presented with fewer complications. A more comprehensive overview of the genetic heterogeneity of the β-thal mutations in the Eastern Province of Saudi Arabia is presented in this article. This study will contribute to the establishment of an effective prevention program, including premarital screening.

Hb Sheffield [β58(E2)Pro→His] in Oman: potential pitfall in genetic counseling

A novel β-globin structural variant, namely Hb Sheffield [β58(E2)Pro→His], was recently found as a sporadic event in a British Subject and posted to the HbVar database (ID 2672). Here we describe the same variant in 11 Omani subjects in the heterozygous state and in one Omani woman in compound heterozygosity with Hb S [β6(A3)Glu→Val]. Hb Sheffield coelutes in the Hb A(2) window in the high performance liquid chromatography (HPLC) system as does Hb E [β26(B8)Glu→Lys], and might be erroneously diagnosed as Hb E unless additional tests including DNA analyses are done. Indeed, correct diagnosis of Hb E is important because of its association with other β-thalassemic and variant alleles can result in relevant clinical conditions, while Hb Sheffield will not. In a genetic (premarital) counseling setting, and in regions where both Hb E ad Hb Sheffield are present, failure to distinguish these variants will represent a serious pitfall.

Global burden, distribution and prevention of β-thalassemias and hemoglobin E disorders

The β-thalassemias, including the hemoglobin E disorders, are not only common in the Mediterranean region, South-East Asia, the Indian subcontinent and the Middle East but have now become a global problem, spreading to much of Europe, the Americas and Australia owing to migration of people from these regions. Approximately 1.5% of the global population are heterozygotes or carriers of the β-thalassemias. While the overall frequencies of carriers of these disorders are known in most countries, there have been few attempts at micromapping and wherever this has been done, significant variations are seen even within small geographic regions. Thus, the figures for the estimated numbers of births each year of homozygous β-thalassemia and the severe compound states involving other hemoglobin disorders may be an underestimate. Screening strategies have varied from premarital to antenatal in different countries depending on socio-cultural and religious customs in different populations. Prenatal diagnosis programs are ongoing in many countries and the knowledge of the distribution of mutations has facilitated the establishment of successful control programs. Many of these were through North-South partnerships and networking. Yet, there are many countries in Asia where they are lacking, and South-South partnerships are now being developed in South-East Asia and the Indian subcontinent to link centers with expertise to centers where expertise needs to be developed. Although the carrier frequencies will remain unaltered, this will eventually help to bring down the burden of the birth of affected children with β-thalassemias and hemoglobin E disorders in Asia.

A descriptive profile of β-thalassaemia mutations in India, Pakistan and Sri Lanka

Thalassaemia is a common and debilitating autosomal recessive disorder affecting many populations in South Asia. To date, efforts to create a regional profile of β-thalassaemia mutations have largely concentrated on the populations of India. The present study updates and expands an earlier profile of β-thalassaemia mutations in India, and incorporates comparable data from Pakistan and Sri Lanka. Despite limited data availability, clear patterns of historical and cultural population movements were observed relating to major β-thalassaemia mutations. The current regional mutation profiles of β-thalassaemia have been influenced by historical migrations into and from the Indian sub-continent, by the development and effects of Hindu, Buddhist, Muslim and Sikh religious traditions, and by the major mid-twentieth century population translocations that followed the Partition of India in 1947. Given the resultant genetic complexity revealed by the populations of India, Pakistan and Sri Lanka, to ensure optimum diagnostic efficiency and the delivery of appropriate care, it is important that screening and counselling programmes for β-thalassaemia mutations recognise the underlying patterns of population sub-division throughout the region.

Molecular bases of beta-thalassemia in the Eastern Province of Saudi Arabia

β-thalassemia is a group of heterogeneous recessive disorders common in many parts of the world. Al-Qatif and Al-Hassa oases in the Eastern Province of Saudi Arabia are regions known for high frequency of these disorders. Using two molecular methods, based on multiplexing-amplification refractory system and reverse hybridization principles, the spectrum of β-thalassemia in the region was studied. Sixty-nine subjects with known β-thalassemia disease and volunteers with high hemoglobin A₂(HbA₂) and low mean corpuscular volume (MCV) were included in this study. Ten mutations were detected in 91% of the subjects under study. Six of these mutations had previously been observed while the other four mutations are reported here for the first time. In addition, four of the mutations accounted for 76.8% of the subjects studied. IVSII-1 (G > A), IVSI-5 (G > A), and codon 39 (C > T) mutations were found to be the most frequent. However, the frequencies of different mutations reported here are slightly different from those reported earlier. A number of these mutations were also found in the neighboring countries, which can be explained in terms of gene flow.

Haematological and clinical features of beta-thalassaemia associated with Hb Dhofar

Hb Dhofar is a variant haemoglobin (beta(29 (GGC-GGT) gly-gly), beta(58 (CCT-CGT) pro-arg)) associated with a thalassaemic phenotype and unique to the Sultanate of Oman. We report clinical and haematological data on 54 subjects with Hb Dhofar (37 heterozygotes, 14 homozygotes and three compound heterozygotes with a different beta-thalassaemia mutation). In heterozygotes, the level of Hb Dhofar ranged from 8.8% to 21.5%. All heterozygotes had Hb A2 > 3.5%, consistent with beta-thalassaemia trait. Hb Dhofar in homozygotes and compound heterozygotes ranged from 26% to 59.7%, with a peripheral film consistent with homozygous beta-thalassaemia. Age at presentation in homozygotes ranged between 6 months and 8 yr, with a majority presenting before 5 yr of age. All had splenomegaly and six (43%) had undergone splenectomy. All had some degree of frontal bossing and in particular, two patients with infrequent transfusions had marked thalassaemic facies and stunting of growth. Hb Dhofar can be mistaken for Hb D as the electrophoretic mobility is similar, but differs from it by a variable and reduced quantity of variant Hb in both heterozygotes and homozygotes. Clinical and haematological data suggest that this mutation behaves like a moderately severe beta(+) thalassaemia allele resulting in a thalassaemia intermedia phenotype.

Molecular basis of thalassemia in Qatar

There is a paucity of information on the molecular basis of beta-thalassemia (thal) in Qatar, a country in the southern part of the Arabian Gulf. To decipher the molecular spectrum of beta- thalassemic alleles present in Qatar, we studied 31 clinically recognized patients, including three with sickle cell disease and beta-thal, and an additional six cases referred for unexplained microcytic anemia. We found 12 different beta-thalassemic alleles and two yet to be defined alleles, mutations likely occurring elsewhere than in the beta-globin gene per se. This is quite striking, given the small size of the study population, and highlights not only the ethnic diversity, but also the necessity of further investigating the thalassemic spectrum.

The Spectrum of beta-Thalassemia Mutations in the Arab Populations

The Arab countries encompass a wide region stretching from the Persian Gulf to the Atlantic Ocean. The Arab population is quite heterogeneous and has experienced various invasions and migrations throughout history. beta-thalassemia is endemic in all countries of the Arab world. Our review of the molecular basis of beta-thalassemia in various Arab countries reveals the presence of 52 mutations, which are mostly of Mediterranean and Asian origin. The distribution of mutations reflects the geographical and historical backgrounds of each region. However, no specific mutation is confined to the Arabs, although some Arab countries do have unique mutations.