An evaluation of inflammatory gene polymorphisms in sibships discordant for premature coronary artery disease: the GRACE-IMMUNE study

Brown et al: BMC Medicine 2010, 8:5 http://www.biomedcentral.com/1741-7015/8/5 Open Access RESEARCH ARTICLE An evaluation of inflammatory gene polymorphisms in sibships discordant for premature coronary artery disease: the GRACE-IMMUNE study Research article Benjamin D Brown1, Jérémie Nsengimana2, Jennifer H Barrett2, Richard A Lawrence1, Lori Steiner3, Suzanne Cheng3, D Timothy Bishop2, Nilesh J Samani4, Stephen G Ball1, Anthony J Balmforth1 and Alistair S Hall*1 Abstract Background: Inflammatory cytokines play a crucial role in coronary artery disease (CAD). We investigated the association between 48 coding and three non-coding single nucleotide polymorphisms (SNPs) from 35 inflammatory genes and the development of CAD, using a large discordant sibship collection (2699 individuals in 891 families). Methods: Family-based association tests (FBAT) and conditional logistic regression (CLR) were applied to single SNPs and haplotypes and, in CLR, traditional risk factors of CAD were adjusted for. Results: An association was observed between CAD and a common three-locus haplotype in the interleukin one (IL-1) cluster with P = 0.006 in all CAD cases, P = 0.01 in myocardial infarction (MI) cases and P = 0.0002 in young onset CAD cases (<50 years). The estimated odds ratio (OR) per copy of this haplotype is 1.21 (95% confidence interval [95CI] = 1.04 - 1.40) for CAD; 1.30 (95CI = 1.09 - 1.56) for MI and 1.50 (95CI = 1.22 - 1.86) for young onset CAD. When sex, smoking, hypertension and hypercholesterolaemia were adjusted for, the haplotype effect remained nominally significant (P = 0.05) in young onset CAD cases, more so (P = 0.002) when hypercholesterolaemia was excluded. As many as 82% of individuals affected by CAD had hypercholesterolaemia compared to only 29% of those unaffected, making the two phenotypes difficult to separate. Conclusion: Despite the multiple hypotheses tested, the robustness of family design to population confoundings and the consistency with previous findings increase the likelihood of true association. Further investigation using larger data sets is needed in order for this to be confirmed. See the related commentary by Keavney: http://www.biomedcentral.com/1741-7015/8/6 Background Coronary atherosclerosis is predominantly an asymptomatic process that progresses over the course of a lifetime. Arterial inflammation is central to plaque progression and plaque rupture with atherosclerotic lesions established as active sites of inflammation [1]. In particular, cytokines appear to coordinate the development of atherosclerosis leading to the formation of complex atherosclerotic plaques. These, in turn, can trigger acute thromboembolic complications such as myocardial infarction (MI) and the * Correspondence: 1Leeds Institute of Genetics, Health and Therapeutics (LIGHT), University of Leeds, UK rupture/repair process that promotes the progression of luminal narrowing [2]. Furthermore, those lesions conveying the greatest risk to the individual are characterized by a higher level of inflammation. Coronary atherosclerosis and its complications are a complex disorder resulting from the combined effects of multiple environmental and genetic factors. Whilst most traditional risk factors for coronary artery disease (CAD) are themselves heritable, a family history remains an independent predictor of this condition [1,2]. The aim of this study was to evaluate individual polymorphisms and haplotypes in inflammatory genes for association with an increased predisposition to CAD. In total, 51 single nucleotide polymorphisms (SNPs) were analysed © 2010 Brown et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Brown et al, BMC Medicine 2010, 8:5 http://www.biomedcentral.com/1741-7015/8/5 in 35 inflammatory genes in a large cohort of discordant sibships recruited across the UK in the Genetic Risk of Acute Coronary Events (GRACE) study. Methods Clinical methods The study was approved by the Multicentre (MREC) and Local Research Ethics Committees (LRECs) throughout the UK. The details of the recruitment process can be found in the Additional File 1. Premature CAD was defined as a validated MI, percutaneous transluminal coronary angioplasty (PTCA), coronary artery bypass surgery (CABG) or angina (exercise test positive or angiogram showing at least one lesion >50%) before the age of 66. Hypercholesterolaemia was considered as either being on lipid lowering therapy or having total cholesterol greater than 4.9 mmol.l-1 for individuals with a previous MI or greater than 5.2 mmol/l for individuals with other affected phenotypes (PTCA, CABG or angina) and unaffected individuals. Hypertension was either being on therapy or a blood pressure greater than 150/90 mmHg. Genotyping Fifty SNPs and one insertion/deletion, mainly located in coding regions of 35 inflammatory genes, were genotyped (48 polymorphisms from coding regions and three from the introns). The primer mix and all other necessary components for the SNP genotyping were provided by Roche Molecular Systems (Pleasanton, USA). Characteristics of the polymorphisms are shown in the Additional File 2. DNA extraction and storage was performed using the PUREGENE® DNA extraction kit (available from Gentra Systems, MN, USA). A pooled polymerase chain reaction (PCR) amplified the chosen targets from 50 ng of genomic DNA to produce biotin labelled products. These products were then hybridized with sequence specific oligonucleotide probes immobilized in a linear array. A series of development stages enabled detection of hybridization between probe and PCR product thus allowing identification of genotypes (homozygous wild, homozygous mutant, heterozygote). The processed strip was then scanned and genotypes were assigned by StripScan software (Roche Molecular Systems) [3] providing a semi-automated reading of the data assigning genotypes. Statistical analyses Family relationships were validated using the Graphical Representation of Relationships (GRR) and RELATIVE programs [4,5] based on the 51 polymorphisms from this study plus 65 additional SNPs (analysis details in the Additional File 3). Allele frequencies were estimated using the program MENDEL which accounts for family relationships [6] and Hardy-Weinberg equilibrium was tested for each SNP using a goodness-of-fit test. The primary analysis was a test of association in presence of linkage between CAD and each individual SNP using the family-based association Page 2 of 12 test (FBAT) [7]. We used the version of this test that employs empirical variance to account for residual familial correlation [8] (program FBAT 2.0.2C, option -e). An additive mode of inheritance was assumed. The analysis was repeated in two s (...truncated)