Hemoglobin alpha 2 gene +861 G>A polymorphism in Turkish population
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Thalassemia is an inherited blood disorder which is divided into two groups: alpha and beta. HBA1 and HBA2 are the two genes associated with alpha thalassemia. The aim of this study is to investigate abnormal hemoglobin variants of alpha globin gene in healthy abnormal hemoglobin carrying individuals with intact beta globin gene. DNA was extracted from peripheral blood samples of seven healthy carrier individuals who have abnormal hemoglobin variants and 16 control individuals from Turkey. Complete coding and intronic sequences of HBA1 and HBA2 genes were amplified by polymerase chain reaction (PCR) and PCR products of HBA1 and HBA2 were sequenced. We were unable to find any base change in our carrier group in the HBA1 gene. We have observed an A/G polymorphism in the downstream untranslated region (+861 G>A) of the HBA2 gene. Our study showed that 14.29% (1/7 carriers) of the carrier group and 37.50% (6/16 controls) of the control group were heterozygous for the +861 G>A polymorphism. The distribution of allele frequencies and genotypes of HBA2 between carrier and control samples were analyzed and it is seen that the distribution of allele frequencies and that of genotypes were not statistically significant between carrier and control samples (P-value = 0.4131, P-value = 0.366, respectively). HBA2 +861 G>A nucleotide substitution is a neutral polymorphism previously reported in other populations. This is the first report in Turkish population.