Abstract
Cases of extreme natural selection could lead either to rapid fixation or extinction of alleles depending on the population structure and size. It may also manifest in excess of heterozygosity and the locus concerned will be displaying such drastic features of allele change. We suspect the 5q31 in chromosome 5 to mirror situation of such extreme natural selection particularly that the region encompasses genes of type 2 cytokine known to associate with a number of infectious and non-infectious diseases.
We typed two sets of single nucleotide polymorphisms (SNPS) in two populations: an initial limited set of only 4 SNP within the genes of IL-4, IL-13, IL-5 and IL-9 in 108 unrelated individuals and a replicating set of 14 SNP in 924 individuals from the same populations with disregard to relatedness. The results suggest the 5q31 area to be under intense selective pressure as indicated by marked heterozygosity independent of Linkage Disequilibrium (LD); difference in heterozygosity, allele, and haplotype frequencies between generations and departure from Hardy-Weinberg expectations (DHWE). The study area is endemic for several infectious diseases including malaria and visceral leishmaniasis (VL). Malaria caused by Plasmodium falciparum, however, occurs mostly with mild clinical symptoms in all ages, which makes it unlikely to account for these indices. The strong selection signals seems to emanate from recent outbreaks of VL which affected both populations to varying extent.