Associations between SDF-1 Alpha Polymorphisms and Malarial Outcomes in Children at Siaya County Referal Hospital, Western Kenya
Otieno, Eric Oloo
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In high Plasmodium transmission regions, malaria caused by Plasmodium falciparum is the leading cause of malaria-related morbidity and mortality among children under the age of 5 years. Severe malaria anaemia (SMA) is the most common cause of malaria burden in holoendemic P. falciparum transmission regions such. Although the mechanisms underlying development of SMA are poorly understood, direct and indirect lysis of erythrocytes, suppression of erythropoiesis, erythrophagocytosis, dyserythropoiesis and dysregulation in pro- and anti-inflammatory response characterize low haemoglobin levels in malaria. Children under the age of 5 years lack naturally-acquired malarial immunity thus innate immunity provides the children with the first line of defence against P. falciparum infections. The risk for progression of malaria infection is partly accounted for by host genetic variations in immune mediators. Stromal cell derived factor (SDF)-1α (CXCL12) is an important mediator of immune, inflammatory and haematopoietic responses. In human malaria, the plasma level of SDF-1α is elevated in children presenting with cerebral malaria and mild-to-moderate anaemia. Even though several studies indicate that SDF-1α genetic variation regulate outcomes of HIV-1 infection, hematopoiesis, and cancer, the role of genetic variability in SDF-1α in P. falciparum infections has not been explored. Genotyping for SDF-1α single nucleotide polymorphisms (SNP) in the promoter (C -1002T; rs2839686) and 3′ UTR (A+801G; rs1801157), DNA was extracted from buccal swabs using the BuccalAmp™ DNA extraction kit (Epicentre Biotechnologies). Genomic DNA was amplified using the Genomiphi DNA amplification kit (GE Healthcare, Life Sciences,Amersham), and then the SNPs were genotyped using a Taqman®5′ allelicdiscrimination Assay-By-Design method according to manufacturer’s instructions (Applied Biosystems). Outcomes of P.falciparum malaria (parasitaemia, high-density parasitaemia, SMA, reticulocyte production index, RPI) in children aged <3 years old (aparasitemic, n=199 and children presenting with P. falciparum non-SMA, n=510 or SMA, n=118) at Siaya County Reffaral, Hospital. Genotype frequencies at the A+801G loci, distribution of major allele A (0.951) and minor allele G (0.049) deviated from Hardy Weinberg Equilibrium (HWE) in the overall study cohort and in each of the study groups (P=0.048). C-1002T genotype frequencies varied significantly among the study groups (TT, 64.9%; CT, 20.1%; and CC, 15.0%; P=0.008). Distribution of major allele T (0.75) and minor allele C (0.25) showed departure from HWE in the overall study cohort and in each of the study groups (P<0.017 for all comparisons). Haplotype analyses identified a total of four haplotypes (AT, AC, GT and GC). Frequencies of haplotypes in overall cohort were (AT, 68.6%; AC, 28.1%; GT, 3.0%, and GC, 0.3%).Evaluation of associations between genotypes and malaria infection status and disease outcomes, indicated that AG genotype at the A+801G loci was significantly associated with about two-times higher odds of having parasitaemia (OR=1.889; P=0.014); but 52% lower odds of developing high- density parasitaemia (OR=0.480; P=0.006). Genotype association with suppression of erythropoiesis showed that AG (OR=1.544; P=0.057) and GG (OR=6.852; P=0.034) genotypes were associated with about one-and-a-half and seven times higher odds of having RPI<2.0, respectively. While at the C-1002T loci, homozygous CC genotype was associated with 43% lower odds of having parasitaemia (OR=0.568; P=0.001). Analysis of the associations of haplotypes showed that AC haplotype carriers were 26% less-likely of having parasitaemia (OR=0.740; P=0.034). GT haplotype carriage was associated with 55% less-likely of having high-density parasitaemia (OR=0.452; P=0.029). GT haplotype was associated with two-times likelihood of having suppression of erythropoiesis (OR=1.979; P=0.026). Taken together, the findings show that genotypic and haplotypic variation at the SDF1α A+801G and C-1002T loci are involved in regulating acquisition of malaria infection and erythropoiesis in children from Siaya region, western Kenya.