Autoimmune diseases and new-onset atrial fibrillation: a UK Biobank study.

AIMS: The underlying mechanisms of atrial fibrillation (AF) are largely unknown. Inflammation may underlie atrial remodelling. Autoimmune diseases, related to increased systemic inflammation, may therefore be associated with new-onset AF. METHODS AND RESULTS: Participants from the population-based UK Biobank were screened for rheumatic fever, gastrointestinal autoimmune diseases, autoimmune diseases targeting the musculoskeletal system and connective tissues, and neurological autoimmune diseases. Between 2006 and 2022, participants were followed for incident AF. Cox proportional hazards regression analyses were performed to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) to quantify associations. 494 072 participants free from AF were included (median age 58.0 years, 54.8% women). After a median of 12.8 years, 27 194 (5.5%) participants were diagnosed with new-onset AF. Rheumatic fever without heart involvement (HR, 95% CI: 1.47, 1.26-1.72), Crohn's disease (1.23, 1.05-1.45), ulcerative colitis (1.17, 1.06-1.31), rheumatoid arthritis (1.39, 1.28-1.51), polyarteritis nodosa (1.82, 1.04-3.09), systemic lupus erythematosus (1.82, 1.41-2.35), and systemic sclerosis (2.32, 1.57-3.44) were associated with a larger AF risk. In sex-stratified analyses, rheumatic fever without heart involvement, multiple sclerosis, Crohn's disease, seropositive rheumatoid arthritis, psoriatic and enteropathic arthropathies, systemic sclerosis and ankylosing spondylitis were associated with larger AF risk in women, whereas only men showed a larger AF risk associated with ulcerative colitis. CONCLUSIONS: Various autoimmune diseases are associated with new-onset AF, more distinct in women. Our findings elaborate on the pathophysiological differences in autoimmunity and AF risk between men and women.

Disentangling the association between kidney function and atrial fibrillation: a bidirectional Mendelian randomization study.

BACKGROUND: The potential bidirectional causal association between kidney function and atrial fibrillation (AF) remains unclear. METHODS: We conducted a bidirectional two-sample Mendelian randomization (MR) analysis. From multiple genome-wide association studies (GWAS), we retrieved genetic variants associated with kidney function (estimated glomerular filtration rate based on creatinine (eGFRcreat), blood urea nitrogen (BUN), chronic kidney disease (CKD stage ≥G3): n = 1,045,620, eGFR based on cystatin C: n = 24,063-32,861, urine albumin-to-creatinine ratio (UACR), and microalbuminuria: n = 564,257), and AF (n = 1,030,836). The inverse-variance weighted method was used as our main analysis. RESULTS: MR analyses supported a causal effect of CKD (n = 9 SNPs, odds ratio (OR): 1.10, 95% confidence interval (CI): 1.04-1.17, p-value = 1.97 × 10-03), and microalbuminuria (n = 5 SNPs, OR: 1.26, 95% CI: 1.10-1.46, p-value = 1.38 × 10-03) on AF risk. We also observed a causal effect of AF on eGFRcreat (n = 97 SNPs, OR: 1.00, 95% CI: 1.00-1.00, p-value = 6.78 × 10-03), CKD (n = 107 SNPs, OR: 1.06, 95% CI: 1.03-1.09, p-value = 2.97 × 10-04), microalbuminuria (n = 83 SNPs, OR: 1.07, 95% CI: 1.04-1.09, p-value = 2.49 × 10-08), and a suggestive causal effect on eGFRcys (n = 103 SNPs, OR: 0.99, 95% CI: 0.99-1.00, p-value = 4.61 × 10-02). Sensitivity analyses, including weighted median estimator, MR-Egger, the MR pleiotropy residual sum and outlier test, and excluding genetic variants associated with possible confounders and/or horizontal mediators (myocardial infarction/coronary artery disease, heart failure) indicated that these findings were robust. CONCLUSIONS: Our results supported a bidirectional causal association between kidney function and AF. The shared genetic architecture between kidney dysfunction and AF might represent potential important therapeutic targets to prevent both conditions in the general population.

Thyroid Signaling, Insulin Resistance, and 2 Diabetes Mellitus: A Mendelian Randomization Study.

Context: Increasing evidence suggests an association between thyroid-stimulating hormone (TSH), free thyroxine (fT4), and deiodinases with insulin resistance and type 2 diabetes mellitus (T2D). Objective: We examined whether TSH and fT4 levels and deiodinases are causally associated with insulin resistance and T2D, using Mendelian randomization. Methods: We selected 20 genetic variants for TSH level and four for fT4 level (identified in a genome-wide association study (GWAS) meta-analysis of European-ancestry cohorts) as instrumental variables for TSH and fT4 levels, respectively. We used summary data from GWASs on the outcomes T2D [Diabetes, Genetics Replication and Meta-analysis (DIAGRAM), n = 12,171 cases and n = 56,862 control subjects] and glycemic traits in patients without diabetes [Meta-Analyses of Glucose and Insulin-Related Traits Consortium (MAGIC), n = 46,186 for fasting glucose and insulin and n = 46,368 for hemoglobin A1c]. To examine whether the associations between TSH/fT4 levels and the study outcomes were causal, we combined the effects of the genetic instruments. Furthermore, we examined the associations among 16 variants in DIO1, DIO2, DIO3, and T2D and glycemic traits. Results: We found no evidence for an association between the combined genetic instrumental variables for TSH and fT4 and the study outcomes. For example, we did not observe a genetically determined association between high TSH level and T2D (odds ratio, 0.91 per standard deviation TSH increase; 95% confidence interval, 0.78 to 1.07). Selected genetic variants in DIO1 (e.g., rs7527713) were associated with measures of insulin resistance. Conclusion: We found no evidence for a causal association between circulatory levels of TSH and fT4 with insulin resistance and T2D, but we found suggestive evidence that DIO1 affects glucose metabolism.