LAUSR

Ample observational evidence indicates that patients with rheumatoid arthritis (RA) are at increased risk of developing comorbid conditions, in particular cardiovascular disease. The pathogenesis of these comorbidities is still largely unknown. For effective preventive measures, it would however be important to discriminate between those that are causally linked with rheumatoid arthritis and those that are the results of concomitant treatments or other confounding factors. Our objective was to explore whether genetically determined manifestation of RA was associated with any comorbidities, in particular cardiovascular disease, by conducting a 2-sample Mendelian randomization (MR) study on publicly available summary statistics from genome-wide association study (GWAS) consortia. Genetic instruments for RA were obtained from a GWAS of 14,361 autoantibody-positive individuals with RA and 43,923 controls of European descent (Okada et al. 2014). The CARDIoGRAMplusC4D consortium comprising 60,801 cases with coronary artery disease and 123,504 controls was used to evaluate the associations with cardiovascular outcomes applying inverse variance–weighted meta-analysis, weighted-median analysis, Mendelian randomization–Egger regression, and multivariable Mendelian randomization. Genetic instruments for RA were further tested for association with other etiologically related traits by using publicly available GWAS data. Genetic predisposition to RA was not associated with higher risk of coronary artery disease (beta coefficient [b] ± standard error [se] = 0.02±0.03; P=0.4913), and myocardial infarction (b ± se = 0.03±0.03; P=0.3338). In contrast, IgA nephropathy (b ± se = 0.47±0.18; P=0.0225) and triglyceride levels were significantly related as outcomes to genetically determined RA as exposure. Other significantly related outcomes were the manifestation of squamous cell lung cancer (b ± se = 0.17±0.08; P=0.0496), serous ovarian cancer (b ± se = 0.13±0.05; P=0.0202), and prostate cancer (b ± se = 0.06±0.02; P=0.0041). Despite the high prevalence of coronary artery disease and myocardial infarction among RA patients in observational studies, cardiovascular outcomes were not significantly associated with RA by Mendelian randomization. This paradox might partly be explained by the traits such as IgA nephropathy and elevated triglyceride levels that could act as mediators for the increased cardiovascular risk by their causal link with genetically determined RA. Type of funding source: Public hospital(s). Main funding source(s): Medical University of Vienna, Austria