Implication effects of imported βs haplotypes on the epidemiology of Plasmodium falciparum infection in eastern Sudan: possible scenario

Abstract

Sickle cell disease is one of the main hereditary diseases in Africa; it arose on at least five different locations. These mutations made the basis of the distinct haplotypes that are linked to the βs gene in different geographical locations. These are identified and numbered as 19, 20, 3, 31 and 17 and are denoted Benin, Bantu, Central African Republic (CAR), Senegal, Saudi Arabia-Indian and Cameroon haplotypes respectively. The evolution of sickle cell disease illustrates the powerful selective pressure of malaria in A frica, where candidate gene association studies have identified more than ten putative susceptibility determinants involving erythrocytes or the immune system. There are many evolutionary forces that resulted in population diversity by affecting the gene frequency of an allele present in that population. The study of genetic geography of HbAS individuals infected with P. falciparum malaria is useful in understanding the patterns and the effects of natural selection on epidemiology of P. falciparum infection in eastern Sudan. HbS gene is one of the genes that are widely assumed to give protection against P. falciparum infection, and confering a survival advantage to individuals possessing it. This study looked into the possible scenario that an immigrant Klan of the Hawsa tribe with their protective haplotypes will ultimately dominate an economically important county in eastern Sudan . Using a non-invasive technique (buccal wash) for samples collection to reduce the risk of blood-transmitted infections, 53 samples were collected and DNA was extracted. Molecular techniques were used to establish the. high prevalence of some βs VI Haplotypes (Cameroon, Car &Benin) in an immigrant group of individual with a symptomatic P. Falciparum infection. The observed Cameroon genotype for the homozygous mutant allele(SS)was seen in13/53 volunteers and the observed genotype for the homozygous of the wild type AA was seen in 17/53.While the observed genotype for the heterozygous(AS) was seen in 23/53 volunteers. Among the total of 53 the frequency of the mutant allele S was calculated as 0.43 and the frequency of wild allele A was 0.57. the CAR haplotype, heterozygous genotype (AS) was seen in 6/10 volunteers tested, the rest were AA and no SS genotype were detected on these volunteers. For the Benin haplotype genotype for the homozygous wild type AA was seen in5/10, while the observed SS genotype for the mutant allele was seen in 3/10 volunteers. The overall prevalence of Hb AS genotype was 43% and Hb SS genotype was 25% giving an HbS gene frequency of 67.9. the observed genotypes were examined to fit the Hardy-Weinberg Equation (HWE) by comparing them with expected values. All results conformed to the Hardy-Weinberg Law when analyzed for the total population sample .the AA,AS,SS genotypes showed p values of 0.9807,0.6337,0.242 respectively. In conclusion ,Hb S haplotypes and especially the Cameroon haplotype are very prevalent in the studied immigrant group of the Hawsa tribe. This could explain the absence of symptomatic malaria.Absence of severe sickle cell anaemia despite the high prevalence of HbS gene in this population defies explanation