Fetal Hemoglobin in Tunisian Sickle Cell Disease Patient: Relationship with Polymorphic Sequences Cis to the ß-Globin Gene.

Fetal hemoglobin (HbF) plays a dominant role in ameliorating morbidity and mortality of hemoglobinopathies. We evaluated the effects of polymorphic markers within the ß-globin gene cluster to identify the genetic mechanics that influence HbF on Tunisian sickling patients (n = 242). Haplotype analysis was carried out by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and the framework polymorphism was established by PCR-sequencing, four independent regions of interest were identified: the 5' region of ß-LCR-HS2 site, the intervening sequence II (IVSII) region of two fetal (Gγ and Aγ) genes and the 5' region of ß-globin gene. The correlation of these various Haplotypes and SNPs with HbF expression and clinical data was studied. Our data showed that among the various polymorphic markers analyzed, only the sequence (AT)xN12(AT)y in LCR HS2 region was significantly associated (p < 0.05) with increased HbF levels, suggesting that the ß-globin gene cluster exerts a significant effect on HbF in sickle cell patients. This study can improve understanding of the physiopathology of the disease and aid to increase our ability to predict clinical severity.

Two new ß+ -thalassemia mutation [ß -56 (G → C); HBBc. -106 G → C] and [ß -83 (G → A); HBBc. -133 G → A] described among the Tunisian population.

OBJECTIVES: Different thalassemia mutations have been reported in various ethnic groups and geographical regions in Tunisia. In the present study, we have investigated two rare ß(+) -thalassemia mutations, that have not previously been reported in the Tunisian population [ß -56 (G > C); HBBc. -106 G > C] and [ß -83 (G > A); HBBc. -133 G > A]. METHODS: The whole ß-globin gene was directly sequenced, and haplotype analysis was conducted through a PCR/RFLP method. RESULTS: Two new mutations were identified for the first time in Tunisia. They are located within the promoter region of ß-globin gene at position -56 (G > C) and -83 (G > A). Linkage analysis using ß-globin gene cluster haplotypes showed that these two mutations were associated with Mediterranean ß-haplotype IX [- + - + + + +] and framework 2 (FW2) [CCTCT]. CONCLUSIONS: The two newly described mutations lead to the ß(+) -thalassemia among Tunisian patients. The haplotype analysis and framework assignment have helped to identify the chromosomal background associated with these mutations, and determine their origin and spread.

Haplotype map of sickle cell anemia in Tunisia.

ß-Globin haplotypes are important to establish the ethnic origin and predict the clinical development of sickle cell disease patients (SCD). To determine the chromosomal background of ß (S) Tunisian sickle cell patients, in this first study in Tunisia, we have explored four polymorphic regions of ß-globin cluster on chromosome 11. It is the 5' region of ß-LCR-HS2 site, the intervening sequence II (IVSII) region of two fetal ((G)γ and (A)γ) genes and the 5' region of ß-globin gene. The results reveal a high molecular diversity of a microsatellite configuration describing the sequences haplotypes. The linkage disequilibrium analysis showed various haplotype combinations giving 22 "extended haplotypes". These results confirm the utility of the ß-globin haplotypes for population studies and contribute to knowledge of the Tunisian gene pool, as well as establishing the role of genetic markers in physiopathology of SCD.