Alpha thalassemia genotypes in Kuwait
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RESEARCH ARTICLE
Open Access
Alpha thalassemia genotypes in Kuwait Adekunle Adekile* , Jalaja Sukumaran, Diana Thomas, Thomas D’Souza and Mohammad Haider
Abstract Background: The frequency of the alpha thalassemia trait is approximately 40% in the Kuwaiti population, but there has been no comprehensive study of the prevalent alleles. This is a report of patients who were referred for molecular diagnosis over a 20-year period. Methods: This is a retrospective study of the α-globin genotypes obtained in the Hemoglobin Research Laboratory of the Department of Pediatrics, Kuwait University from 1994 to 2015. Genotyping was performed by a combination of PCR, allele-specific oligonucleotide hybridization and reverse dot blot hybridization (Vienna Lab Strip Assay). Results: Four hundred samples were characterized and analyzed from individuals aged < 1 month to 80 years, with a median of 6 years from 283 unrelated families. Most (90.8%) were Kuwaiti nationals. The commonest genotype was homozygosity for the polyadenylation-1 mutation (αPA-1α/α PA-1α) in 33.3% of the samples, followed by heterozygosity (αα/α PA-1α) for the same mutation in 32.3%. PA-1 was therefore the most frequent allele (0.59). The frequency of the α0 (−-MED) allele was 0.017. Rare alleles that were found in very low frequencies included α0 (−-FIL) in a Filipino child, Hb Constant Spring, Hb Adana, and Hb Icaria. Conclusion: There is a wide variety of alpha thalassemia alleles among Kuwaitis, but nondeletional PA-1 is by far the most common cause of the moderate to severe HbH (β4 tetramer) disease phenotype. The α0 (−MED) allele is also encountered, which has implications for premarital counseling, especially for the possibility of having babies with alpha thalassemia major (Barts hydrops fetalis). Keywords: Alpha thalassemia, Hemoglobin H disease, Kuwait
Background Alpha thalassemia is one of the most widespread genetic diseases worldwide, with frequencies of the carrier state reaching up to 80–90% in some areas [1]. The incidence is approximately 25–30% in tropical Africa [2], while in the Arabian Peninsula, the frequency varies from a low of close to zero in the desert areas to as high as 60% in the agricultural zones of Eastern Saudi Arabia [3, 4]. The normal individual has a complement of four αglobin genes (αα/αα), any one of which can be absent, producing varying degrees of alpha thalassemia [1]. In α0 alleles, both genes on a chromosome are deleted (--), while in α+, a variable portion of the α2 and/or α1 gene is * Correspondence: [email protected] Department of Pediatrics, Faculty of Medicine, Kuwait University, PO Box 24923, 13110 Safat, Kuwait
deleted, resulting in a reduction in chain synthesis. The size of the deletion in α0 alleles is variable, and each is named for the part of the world where it is prevalent. Thus --MED,(--)FIL, and --SEA deletions are found in the Mediterranean, Philippines and South East Asia, respectively [5]. The α+ deletions are designated by their sizes, and the most common is the –α-3.7 kb allele. One- or 2gen
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