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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 8  |  Issue : 3  |  Page : 99-104

Molecular patterns of β-thalassemia mutations of Saudi patients referred to King Faisal Specialist Hospital and Research Center


1 Hematology Section, Pathology Department, King Fahad Central Hospital, Ministry of Health, Jazan, Saudi Arabia
2 King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
3 Department of Pathology and Laboratory Medicine, King Khalid University Hospital, Riyadh, Saudi Arabia

Date of Web Publication18-Sep-2017

Correspondence Address:
Ayman Mashi
Hematology Section, Pathology Department, King Fahad Central Hospital, Ministry of Health, Jazan
Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/joah.joah_61_16

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  Abstract 

Background: Beta thalassemias are a group of hereditary blood disorders that are characterized by reduction or complete absence of the β-globin chain synthesis due to mutations, affecting critical areas of the β-globin gene on the chromosome 11. The disease is inherited in an autosomal recessive manner, with severity ranging from asymptomatic individuals to transfusion dependent anemia, according to the nature of the mutation. The prevalence of the β-globin gene in various areas of Saudi Arabia, previously reported as 0.01 to 0.15% in general population.
Materials And Methods: A cohort of 131 samples, which were submitted for β-globin gene mutation analysis in King Faisal Specialist Hospital and Research Center during 2008 to 2013, were tested for the entire genomic region (3-Exons and 2-Introns) of the HBB gene by direct Sanger sequencing technique.
Results: Out of the total population tested, 28 (21%) were undetectable cases and 103 (79%) were detectable for β-globin chain mutations. Nineteen different mutations of the HBB gene were identified in all detectable cases (103 patients). Among these mutations c.315+1G>A, c.118C>T, and c.92+5G>C were detected in the majority of cases (66%) with five novel mutations (c.410G>A, c.-151C>T, c.68_74delAAGTTGG, c.316-3C>A, and c.-31C>T) that are reported for the first time in Saudi population.
Discussion: The result of this retrospective study confirms the previously reported common β-thalassemia mutations among Saudi population.

Keywords: Autosomal recessive, HBB, sequencing, thalassemias


How to cite this article:
Mashi A, Khogeer H, khyatte A, Abalkhail H, Khalil S. Molecular patterns of β-thalassemia mutations of Saudi patients referred to King Faisal Specialist Hospital and Research Center. J Appl Hematol 2017;8:99-104

How to cite this URL:
Mashi A, Khogeer H, khyatte A, Abalkhail H, Khalil S. Molecular patterns of β-thalassemia mutations of Saudi patients referred to King Faisal Specialist Hospital and Research Center. J Appl Hematol [serial online] 2017 [cited 2017 Oct 24];8:99-104. Available from: http://www.jahjournal.org/text.asp?2017/8/3/99/215001




  Introduction Top


β-Thalassemia syndromes are a group of hereditary disorders characterized by a genetic mutation that leads to a complete absence, or severe or mild deficiency of β-globin chains synthesis. The complete absence or severe deficiency results in thalassemia major or thalassemia intermedia.[1],[2]

Homozygous and compound heterozygous state (thalassemia major/intermedia) causes severe, transfusion-dependent anemia, whereas heterozygous state (β-thalassemia trait) causes mild-to-moderate microcytic anemia. The molecular bases of β thalassemia are very heterogeneous. The great majorities of β-thalassemia cases are caused by point mutations, affecting the coding region of critical areas of the β-globin gene and are only rarely produced by gross-gene rearrangements.[2]

Mutations causing complete inactivation of β genes (such as deletion, initiation codon, nonsense, frameshift, or splicing mutations) will make the gene unable to produce any β-globin chain resulting in β0 thalassemia. Although some other mutations cause partial inactivation of the β genes causing reduction in β-globin chain synthesis resulting in β+ or β++ (silent), thalassemia depends on the degree of reduction of the β chains production.[2],[3]

Absence or reduction of β-globin chain will increase the accumulation of free α chain within the erythroblasts and the red blood cells. The major consequences of this pathophysiology are ineffective erythropoiesis, splenomegaly, and tissue hypoxia due to increased hemoglobin F and deformities of the skull and facial bone marrow. The severity of the disease differs according to the ratio between α-globin/non-α-globin chain synthesis and excessing in free α-chain.[2]

The β-globin (HBB) genes are located in the short arm of chromosome 11 and controlled by single locus control region. The HBB gene contains three exons, two introns, and both 5′ and 3′ untranslated regions as well as it contains 146 amino acids with a molecular weight of around 1.6 Kb.[3]

Worldwide, 3% of the populations (~150 million people) are carriers of the β-thalassemia gene.[4],[5]

Over 300 mutations in β-globin gene have been characterized globally with a subset of ~40 mutations responsible for the majority of cases, according to population studies.[2],[6],[7]

The mutations are population specific and each country has its own unique and frequency of β-globin mutations. The prevalence of β thalassemia is high in Mediterranean countries, the Middle East, Central Asia, India, Southern China, and the Far East as well as countries along the north coast of Africa, and in South America. In addition, it is encountered in diverse frequencies in all Arab countries with carrier rate of 1 to 11%.[8] The prevalence of β thalassemia in Saudi Arabia varied significantly in different parts of the country, with the highest prevalence being in the Eastern province of the country (around Jubail, Qateef, Dammam, and Hofuf) and along the coastal strip of the Red Sea.[9],[10],[11]


  Materials and Methods Top


Samples submitted for molecular screening for β thalassemia during the past 6-year period, 2008 to 2013 from the Medical Genetics and Hematology clinics in King Faisal Specialist Hospital and Research Center (KFSH & RC) (General Organization), Riyadh. Patients who were diagnosed with β thalassemia through clinical suspicion, family history, and have hypochromic microcytic anemia and/or high HbA2 or HbF level in hemoglobin electrophoresis were included for analysis. Family studies were excluded from this cohort.

This retrospective review study was approved by the Research Advisory Council and the hospital ethical committee under the RAC# 2131152. The samples represent cases from all over the kingdom that is referred to KFSH & RC for treatment options. Selection criteria were applied.

DNA Extraction and Sequencing

The genomic DNA was extracted by MagNA pure system (Roche Diagnostics, Mannheim, Germany) from EDTA-blood sample and amplified by PCR. Comprehensive sequence analysis of the β-globin gene was carried out. Sample was tested for the entire genomic region (3-Exons and 2-Intron) of the HBB gene, including 100 nucleotide upstream and downstream from the coding sequences. DNA sequences of the PCR products were amplified by using four primer pairs for HBB gene and determined by using BigDye Terminator v3.1 cycle sequencing ready reaction kit (Applied Biosystems, Foster City, California, USA) and analyzed on an ABI 3730XL automated sequencer from both strands ABI 3730xl Genetic Analyzer (Applied Biosystems, Foster City, CA). Analysis and mutation nomenclature were based on GenBank Accession NM_000518.4. The data were collected through the information system.


  Results Top


This study was carried out on a total number of 131 patients who were recruited for clinical investigation from the Hematology clinic at KFSH & RC for a 6-year period. Out of the total population, 28 (21%) were undetectable cases and 103 (79%) were detectable cases for β globin chain mutations.

The male gender represented 57/131 patients (43.5%), whereas female patients were 74/131 (56.5%). The patients were distributed into two major groups according to their age: pediatric group 15 years or less (52%) and adult group more than 15 years (48%). [Table 1] and [Table 2] show the distribution of all analyzed cases and the detectable cases, respectively, according to their age group.
Table 1: The frequency of β-thalassemia mutations

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Table 2: The comparison between current data and the previous studies

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Detectable cases (103 patients) were categorized into three groups according to allele zygosity: homozygous, heterozygous, and compound heterozygous; 47 (45.6%), 41 (39.8%), and 15 (14.6%), respectively. The majority of homozygous cases are discovered in pediatric age group, whereas the majority of adult cases are heterozygous.

Nineteen mutations were identified in all detectable (103 patients) cases that are illustrated in [Table 1].

Three mutations (c.315+1G>A, c.118C>T, and c.92+5G>C) were detected in the majority of cases (66%). The c.315+1G>A, previously known as IVS-II-1G>A, is a splicing mutation that was most frequently encountered in our study with a frequency of 32%. Followed by truncating nonsense mutation, the c.118C>T (previously known as Q39X or p. Gln 40X) 23% and the c.92+5G>C (previously known as IVS-I-5G>C) 11%. The c.315+1G>A and c.118C>T mutations were common in homozygous cases, whereas c.92+5G>C was more common in compound heterozygous cases.

The c.93-21_del 25bp, c.79G>A, c.93-21G>A, and c.92+1G>A were identified in 7, 7, 5, and 4%, respectively [Table 1].

The c.92+6T>C, c.25-26 delAA, c.27-28insG, and c.-137C>T mutations are detected in 3% of cases for each one [Table 1].

Four mutations, including c.-151C>T, c.17_18delCT, c.135delC, and c.93-1G>C, are reported only in 2% of cases [Table 1].

Five novel mutations (c.410G>A, c.-31C>T, c.68_74delAAGTTGG, c.316-3C>A, and c.-151C>T) were identified for the first time in Saudi population. The former three mutations represent 1% of cases for each, whereas the later presented with a frequency of 2% [Table 1].


  Discussion Top


In general, β thalassemia primarily affects people of Mediterranean and Middle Eastern ethnicity, including the Gulf region. The eastern (Al-Qatif and Al-Ahsa) and western (region along the coastal strip of the Red Sea) provinces of Saudi Arabia are known for high prevalence of β-thalassemia.[9],[12],[13]

β-Globin gene mutations are different in various regions worldwide and between ethnic groups, and many of these mutations have been reported in Saudi Arabia.

In the past, some of studies screened specific reported mutations in the β-globin gene to assess their presence and frequencies in Saudi patients.[14],[15],[16],[17]

More recent studies were conducted to provide a precise figures and frequencies of the β-thalassemia mutations in specific region of Saudi Arabia.[12],[13],[18],[19] All previous studies that reported different β-globin gene mutations in Saudi Arabia are summarized in [Table 2].

Abuzenadah et al. have recently identified 23 mutations responsible for β-thalassemia in western region of Saudi Arabia. Of these, there were seven common mutations with the most frequent one being IVS-I-5G>C [Table 2] and the other 16 mutations were less common, including one new mutation that has never been reported in the Saudi Arabia, the FSC 20/21 mutation.

In other recent studies reported from the Eastern Province of Saudi Arabia by Al-Sultan et al., 14 mutations were identified. Among these, there were five frequent mutations with the more common one being IVS-II-1G>A [Table 2]. The author reported two novel mutations IVS-I-130 (G → C) and IVS-I-110 (G → A), which have not been previously reported in the population of the Eastern Province.

A total of 12 different mutations were reported in one more recent study from Riyadh by Warsy et al., in which the IVS-I-5G>C mutation was the most common [Table 2].

In this study, we present a comprehensive report on the spectrum of β-thalassemia mutations. Given that, KFSH and RC represents a tertiary specialized hospital in Saudi Arabia in which advance molecular technologies are available for detecting wide range of molecular abnormalities.

Our study more and less shows similar findings that had been observed by previous studies. A total of 19 mutations were identified in this retrospective report. Out of these, 14 mutations have been reported in the previous studies that have been conducted in Saudi Arabia and five novel mutations were reported for the first time in Saudi population [Table 2].

It has been noticed that the frequencies and prevalence of the 14 mutations are different among the Saudi population who screened for these mutations in the previous studies. This diversity is mainly due to the unique geographical position of Saudi Arabia that lie between the Mediterranean and Southeast Asian region. The most frequent mutations in our study are c.315+1G>A, c.118C>T, and c.92+5G>C. These findings were also reported by most of studies on Saudi population with differences in their frequencies. The clinical significance of c.315+1G>A and c.118C>T mutations is their ability to produce the β0 thalassemia phenotype. These mutations were reported to occur in most of the Mediterranean and Gulf countries (Warsy, Abuzenadah, Sultan, Ali), although the c.92+5G>C produces β+ thalassemia phenotype and frequently encountered in Asian Indian. In comparing our data to previous studies, we found that five mutations appear to be fingerprints of Saudi population and were most frequently reported in all studies [Table 2]. These mutations are c.315+1G>A, c.118C>T, c.92+5G>C, c.93-22_del 25bp, and c.93-21G>A, which are reported in almost all of studies [Figure 1].
Figure 1: The most common five β-globin gene mutations in Saudi Arabia

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We report five novel mutations (c.410G>A, c.-31C>T, c.68_74delAAGTTGG, c.316-3C>A, and c.-151C>T), which to the best of our knowledge, have not been described in Saudi Arabia [Table 1] and [Table 2].

In summary, this comprehensive analysis successfully identified 19 mutations, five of which are novel, and confirmed the previously published mutations among the Saudi population. The potential outcome of this study is to publish a list of more frequent β-globin gene mutations in Saudi β-thalassemia patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Abuzenadah AM, Hussein IM, Damanhouri GA, A-Sayes FM, Gari MA, Chaudhary AG, et al. Molecular basis of β-thalassemia in the western province of Saudi Arabia: Identification of rare β-thalassemia mutations. Hemoglobin 2011;35:346-57.  Back to cited text no. 13
    
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    Tables

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