[Hemoglobin beta S haplotype in the Kebili region (southern Tunisia)]

Sickle cell anemia is a monogenic hereditary disease characterized by a mutation in the beta globin gene. Five major haplotypes associated with the beta S mutation have been defined: Benin, Bantu, Senegalian, Camerounian, and Arabo-Indian. Previous studies in northern Tunisia showed that sickle cell anemia was of Benin origin in this region. Patients from the south of Tunisia, mainly from the Kebili region, were not previously concerned. In this study, we have determined the beta S haplotype and evaluated phenotypical expression of the disease in 14 patients from this latter region. The use of four restriction endonucleases having polymorphic sites in the beta globin gene showed that all patients had the Benin haplotype, confirming the Benin origin of sickle cell anemia in Tunisia. This haplotype is associated with an heterogeneous expression of fetal hemoglobin (HbF) with extremes varying from 2.4 to 16.3% and a mean expression rate of 8.16%, which is in accordance with literature data. In spite of the haplotype homogeneity in our patients, clinical heterogeneity was noted. A unique case of alpha-thalassemia could not explain this heterogeneity. In contrast, we found a certain correlation between fetal hemoglobin expression and clinical severity.