case-control approach to identify plasmodium falciparum polymorphisms associated with severe malaria病例对照方法识别恶性疟原虫多态性与严重的疟疾.pdf

Case-Control Approach to Identify Plasmodium falciparum Polymorphisms Associated with Severe Malaria Watcharee Chokejindachai1,2, David J. Conway1,3* 1 Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom, 2 Department of Tropical Pediatrics, Faculty of Medicine, Mahidol University, Bangkok, Thailand, 3 Medical Research Council Laboratories, Fajara, Banjul, The Gambia Abstract Background: Studies to identify phenotypically-associated polymorphisms in the Plasmodium falciparum 23 Mb genome will require a dense array of marker loci. It was considered promising to undertake initial allelic association studies to prospect for virulence polymorphisms in Thailand, as the low endemicity would allow higher levels of linkage disequilibrium (LD) than would exist in more highly endemic areas. Methodology/Principal Findings: Assessment of LD was first made with 11 microsatellite loci widely dispersed in the parasite genome, and 16 microsatellite loci covering a ,140 kb region of chromosome 2 (an arbitrarily representative non- telomeric part of the genome), in a sample of 100 P. falciparum isolates. The dispersed loci showed minimal LD (Index of Association, ISA = 0.013, P = 0.10), while those on chromosome 2 showed significant LD values mostly between loci ,5 kb apart. A disease association study was then performed comparing parasites in 113 severe malaria cases and 245 mild malaria controls. Genotyping was performed on almost all polymorphisms in the binding domains of three erythrocyte binding antigens (eba175, eba140 and eba181), and repeat sequence polymorphisms ,2 kb apart in each of three reticulocyte binding homologues (Rh1, Rh2a/b, and Rh4). Differences between cases and controls were seen for (i) codons 388-90 in eba1