Associations Of The Interleukin 17A/17F/18 Gene Cluster With Myocardial Infarction In Northern Chinese Han Population

Myocardial infarction (MI), one of the leading causes of death worldwide, is a complex disorder influenced by multiple genetic factors and environmental factors. Approximately 90% of MI results from an acute thrombus that obstructs an atherosclerotic coronary artery. There is growing evidence that inflammation plays a key role in the formation and development of atherosclerotic lesions, plaque vulnerability and rupture, and thrombogenicity. Interleukin (IL)-17A, IL-17F and IL-18 which are newly pleiotropic proinflammatory cytokines was found, has been shown to contribute to coronary heart disease and its sequelae in recent years. Over the past years, the polymorphisms of IL-17A, IL-18 (-607C/A and -137G/C), and IL-17F (His161Arg) have been studied in many inflammatory diseases such as asthma, rheumatoid arthritis, and inflammatory bowel disease. However, few studies have evaluated the association between MI and these polymorphisms. So the aim of the present study was to scan the whole IL-17A gene to identify all putative functional polymorphisms and further to investigate whether these polymorphisms are associated with MI in northern Chinese Han population. In addition, the polymorphisms of IL-18 (-607C/A and -137G/C) and IL-17F (His161Arg) were genotyped directly. In the study, we also further investigated whether these polymorphisms were related to MI in our population.A total of 990 unrelated subjects, including patients with MI (n=513) and age- and sex- matched control subjects (n=477), were enrolled in the present study. All subjects were Han Chinese from the northern region of China and randomly selected from the Department of Cardiology of Shenyang Northern Hospital between 2005 and 2008. We initially selected 48 unrelated individuals from our case group to detect all polymorphism of the IL-17A gene by directly sequencing of genomic DNAs. Sequently, six polymorphisms with minor allele frequencies (MAF) > 0.05 were selected for genotyping by directly sequencing in 468 patients with MI and 440 sex- and age-matched control subjects drawn from the total sample.The IL-17F His161Arg polymorphism were determined by polymerase chain reactionsequence- restriction fragment length polymorphism (PCR-RFLP) analysis in the all subjects. The polymorphisms at positions -607 and -137 in the IL-18 gene promoter were genotyped using polymerase chain reactionsequence-sequence specific primers (PCR-SSP) technique only in 234 patients with MI and 216 sex- and age-matched control subjects from the total sample. Theχ2-test and univariate analysis was applied to measure the association of each single polymorphism with MI. Multivariate analysis was performed to investigate the independent effect between the polymorphisms and MI. We obtained estimates of pairwise linkage disequilibrium (LD) values using Haploview program. The extent of pairwise linkage disequilibrium was expressed in terms of D', and the pairwise correlation was presented as r2. Haplotype estimation and inference was determined using PHASE v2.2.1. based on the whole sample population. Retrospective statistical powers were calculated using QUANTO software.The main results of our study were listed as follow:1. IL-17A polymorphisms and MI:①In a total of 3691bp explored, we indentified 10 single nucleotide polymorphism (SNPs), of which, 3 were first reported reported (with MAF<5%). Of the seven remaining SNPs, six were in 5′region, one was in intron 1;②Allele frequencies of some polymorphisms might vary among different ethnic groups. For example, the frequencs of -877 G allele were reported to be 0.73 and 0.24 in Caucasian populations and Japanese populations, respectively, whereas in our population, this allele has a frequency of 0.31;③Complete or nearly complete LD between polymorphisms was frequently observed. For instance, the -121G/A and -197G/A polymorphisms were almost completely LD;④Both univariate and multivariate analyses indicated that the IL-17A polymorphisms were not associated with MI in our population. Further stratification for age, gender, the number of diseased coronary arteries and other cardiovascular risk factors did not affect the negative findings. Finally, a haplotype-based analysis of IL-17A SNPs also failed to detect an association with MI.2. IL-17F His161Arg polymorphism and MI:①The prevalence of the IL-17F His161Arg polymorphism varies across races and ethnicities. In our control subjects, the C allele frequency was observed to be 0.11, which was similar to those observed in Korean and Japanese populations (0.10-0.13) and was higher than those of Caucasians (0.03-0.05). ②Both univariate and multivariate analyses failed to detect that the IL-17F His161Arg polymorphism was associated with MI in our population. Further stratification for age, gender, the number of diseased coronary arteries and other cardiovascular risk factors did not affect the negative findings.3. IL-18 -607C/A and -137G/C polymorphisms and MI:①The distribution of gene variations may be greatly different between various populations. In this study, the frequencies of the -607A and -137C alleles among the controls were 0.54 and 0.15, respectively, and these were similar to those frequencies observed in Korean (0.51, 0.11) and Japanese population (0.61, 0.14); however, the frequencies were significantly different from those of European Caucasians (0.44, 0.28) and Africans (0.44, 0.29);②Both univariate and multivariate analyses indicated that the -607C/A polymorphism was associated with MI, in contrast with -137G/C variant. Compared with the -607AA homozygote, the odds ratio (OR) was 1.89 for the -607C allele carriers;③The two polymorphisms studied were found to be in LD. Mainly four haplotypes, namely AC, AG, CC, and CG(in the order of -607C/A, -137G/C)were estimated based on the genotype data of the two variants. Among estimated haplotypes, CG was independently associated with a significantly increased risk of MI, in contrast with AC. (adjusted OR=1.601 and 0.531, respectively).In conclusion, based on SNP discovery and population genetic analysis, the present association study suggests that the -607C/A polymorphism of IL-18 and/or its related haplotype significantly associated with the risk of MI in northern Chinese Han population. However, our results do not support a major involvement of IL-17F and IL-17A polymorphisms, associated with other inflammatory diseases in predisposition to MI. To fully exclude a smaller effect of these variants in MI susceptibility, further studies are needed in a large dataset from other populations.