Restriction mapping of βS locus among Tunisian sickle-cell patients.

Objectives: The polymorphism of the β-globin gene haplotypes and frameworks is useful in the determination of the unicentric and multicentric origin of a mutational event. In our study, the haplotypes linked to the Tunisian β(S) mutation are determined to improve our knowledge of the chromosomal background of the β-globin gene in sickle-cell anemia in Tunisia.

Methods: The authors have investigated 242 unrelated individuals. Haplotype analysis was carried out by polymerase chain reaction-restriction fragment length polymorphism-based methods. Seven polymorphic sites in the β-globin gene cluster were examined. The correlation of these various haplotypes with Hb F expression was studied.

Results: The Benin haplotype (Ben) was largely predominant (60.54%) followed by the Atypical haplotype A (8.43%) and Bantu (Ban) (2.71%) haplotypes. A total of 94 chromosomes had atypical haplotypes, 78 (23.49%) had A1 [-----++], 11 (3.31%) had A2 [-------], and five (1.5%) had B1 [--+--++]. The Benin haplotype is associated with a fairly low HbF levels.

Conclusion: The very high frequency of the Benin haplotype in our study suggests that the β(S) mutation present in Tunisia may have originated from the Benin region and was brought to Tunisia along the slave trade routes. However, another atypical haplotype observed a new emergence in our population and could be considered as specific to Tunisian chromosome β(S).