ABSTRACT
Fetal hemoglobin (HbF), encoded by the HBG2 and HBG1 genes, is the best-known genetic modulator of sickle cell anemia, varying dramatically in concentration in the blood of these patients. This variation is partially associated with polymorphisms located in the promoter region of the HBG2 and HBG1 genes. In order to explore known and unknown polymorphisms in these genes, the sequences of their promoter regions were screened in sickle cell anemia patients and correlated with both their HbF levels and their ÀS-globin haplotypes. Additionally, the sequences were compared with genes from 2 healthy groups, a reference one (N = 104) and an Afro-descendant one (N = 98), to identify polymorphisms linked to the ethnic background.The reference group was composed by healthy individuals from the general population. Four polymorphisms were identified in the promoter region of HBG2 and 8 in the promoter region of HBG1 among the studied groups. Four novel single nucleotide polymorphisms (SNP) located at positions -324, -317, -309 and -307 were identified in the reference group. A deletion located between -396 and -391 in the HBG2 promoter region and the SNP -271 C¨T in the HBG1 promoter region were associated with the Central African Republic ÀS-globin haplotype. In contrast, the -369 C¨G and 309 A¨G SNPs in the HBG2 promoter region were correlated to the Benin haplotype. The polymorphisms -396_-391 del HBG2, -369 SNP HBG2 and -271 SNP HBG1 correlated with HbF levels. Hence, we suggest an important role of HBG2 and HBG1 gene polymorphisms on the HbF synthesis.
Subject(s)
Aged , Child , Female , Humans , Male , Anemia, Sickle Cell/genetics , Polymorphism, Genetic/genetics , Promoter Regions, Genetic/genetics , gamma-Globins/genetics , Black People , Anemia, Sickle Cell/blood , Brazil , Genotype , HaplotypesABSTRACT
The fetal hemoglobin (HbF) levels and betaS-globin gene haplotypes of 125 sickle cell anemia patients from Brazil were investigated. We sequenced the Gg- and Ag-globin gene promoters and the DNase I-2 hypersensitive sites in the locus control regions (HS2-LCR) of patients with HbF level disparities as compared to their ßS haplotypes. Sixty-four (51.2 percent) patients had CAR/Ben genotype; 36 (28.8 percent) Ben/Ben; 18 (14.4 percent) CAR/CAR; 2 (1.6 percent) CAR/Atypical; 2 (1.6 percent) Ben/Cam; 1 (0.8 percent) CAR/Cam; 1 (0.8 percent) CAR/Arab-Indian, and 1 (0.8 percent) Sen/Atypical. The HS2-LCR sequence analyses demonstrated a c.-10.677G>A change in patients with the Ben haplotype and high HbF levels. The Gg gene promoter sequence analyses showed a c.-157T>C substitution shared by all patients, and a c.-222_-225del related to the Cam haplotype. These results identify new polymorphisms in the HS2-LCR and Gg-globin gene promoter. Further studies are required to determine the correlation between HbF synthesis and the clinical profile of sickle cell anemia patients.