Structural and Functional Insights on an Uncharacterized Aγ-Globin-Gene Polymorphism Present in Four β0-Thalassemia Families with High Fetal Hemoglobin Levels

Several DNA polymorphisms have been associated with high production of fetal hemoglobin (HbF), although the molecular basis is not completely understood. In order to identify and characterize novel HbF-associated elements, we focused on five probands and their four families (from Egypt, Iraq and Iran) with thalassemia major (either beta(0)-IVSII-1 or beta(0)-IVSI-1) and unusual HbF elevation (> 98 %), congenital or acquired after rejection of bone marrow transplantation, suggesting an anticipated favorable genetic background to high HbF expression. Patient recruitment, genomic DNA sequencing, western blotting, electrophoretic mobility shift assays, surface plasmon resonance (SPR) biospecific interaction analysis, bioinformatics analyses based on docking experiments. A polymorphism of the A gamma-globin gene is here studied in four families with beta(0)-thalassemia (beta(0)-IVSII-1 and beta(0)-IVSI-1) and expressing unusual high HbF levels, congenital or acquired after rejection of bone marrow transplantation. This (G -> A) polymorphism is present at position +25 of the A gamma-globin genes, corresponding to a 5'-UTR region of the A gamma-globin mRNA and, when present, is physically linked in chromosomes 11 of all the familiar members studied to the XmnI polymorphism and to the beta(0)-thalassemia mutations. The region corresponding to the +25(G -> A) polymorphism of the A gamma-globin gene belongs to a sequence recognized by DNA-binding protein complexes, including LYAR (Ly-1 antibody reactive clone), a zinc-finger transcription factor previously proposed to be involved in down-regulation of the expression of gamma-globin genes in erythroid cells. We found a novel polymorphism of the A gamma-globin gene in four families with beta(0)-thalassemia and high levels of HbF expression. Additionally, we report evidence suggesting that the A gamma-globin gene +25(G -> A) polymorphism decreases the efficiency of the interaction between this sequence and specific DNA binding protein complexes.