The effects of old and recent migration waves in the distribution of HBB*S globin gene haplotypes

Abstract

Sickle cell hemoglobin is the result of a mutation at the sixth amino acid position of the beta (β) globin chain. The HBB*S gene is in linkage disequilibrium with five main haplotypes in the β-globin-like gene cluster named according to their ethnic and geographic origins: Bantu (CAR), Benin (BEN), Senegal (SEN), Cameroon (CAM) and Arabian-Indian (ARAB). These haplotypes demonstrated that the sickle cell mutation arose independently at least five times in human history. The distribution of βS haplotypes among Brazilian populations showed a predominance of the CAR haplotype. American populations were clustered in two groups defined by CAR or BEN haplotype frequencies. This scenario is compatible with historical records about the slave trade in the Americas. When all world populations where the sickle cell gene occurs were analyzed, three clusters were disclosed based on CAR, BEN or ARAB haplotype predominance. These patterns may change in the next decades due to recent migrations waves. Since these haplotypes show different clinical characteristics, these recent migrations events raise the necessity to develop optimized public health programs for sickle cell disease screening and management.

Figure 1. PCA based on F_ST distances calculated using haplotype frequencies showing clustering patterns for different Brazilian populations according to HBB*S haplotypes.

Figure 2. PCA based on F_ST distances calculated using haplotype frequencies showing clustering patterns for different American populations according to HBB*S haplotypes.

Figure 3. PCA based on F_ST distances calculated using haplotype frequencies showing clustering patterns for different world populations according to HBB*S haplotypes.

Figure 4. World map showing the main migrations concerning HBB*S dispersion. The full lines represent the old migrations, while the dotted lines represent recent migrations.