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The clinical presentation of b-thalassemia intermedia phenotypes are influenced by many factors .The persistence of fetal hemoglobin and several polymorphisms located in the promoters of g- and b-globin genes are some of them .The aim of this study was to evaluate the combined effect of the -158Gg (CàT) polymorphism and of the (AT)x(T)y configuration, as well as their eventual association with elevated levels of HbF in b-thalassemia carriers, b-thalassemia Intermedia , b-thalassemia major and normal controls of Indian origin. The -158 Gg T allele was found to be associated with increased levels of HbF in b-thalassemia carriers, and not in wild-type subjects. In the homozygous group the -158 Gg T allele was significantly higher in the thalassemia intermedia group (66%) as against the thalassemia major group (21%). The (AT)9(T)5 allele did not show any association with raised HbF levels. However 24% of milder cases showed presence of this allele.
This study suggests that two regions of the b globin cluster, whether in cis or in trans to each other, can interact to enhance HbF expression when a b thalassemic determinant is present in heterozigosity and help in amelioration of the severity of the disease in homozygotes.