title: Does elevated C-reactive protein increase atrial fibrillation risk? A Mendelian randomization of 47,000 individuals from the general population.
abstract: OBJECTIVE
  The purpose of this study was to test whether the association of C-reactive protein (CRP) with increased risk of atrial fibrillation is a robust and perhaps even causal association.
  
  
  BACKGROUND
  Elevated levels of CRP previously have been associated with increased risk of atrial fibrillation.
  
  
  METHODS
  We studied 10,276 individuals from the prospective Copenhagen City Heart Study, including 771 individuals who had atrial fibrillation during follow-up, and another 36,600 persons from the cross-sectional Copenhagen General Population Study, including 1,340 cases with atrial fibrillation. Individuals were genotyped for 4 CRP gene polymorphisms and had high-sensitivity CRP levels measured.
  
  
  RESULTS
  A CRP level in the upper versus lower quintile associated with a 2.19-fold (95% confidence interval [CI]: 1.54- to 3.10-fold) increased risk of atrial fibrillation. Risk estimates attenuated slightly after multifactorial adjustment to 1.77 (95% CI: 1.22 to 2.55), and after additional adjustment for heart failure and plasma fibrinogen level to 1.47 (95% CI: 1.02 to 2.13) and 1.63 (95% CI: 1.21 to 2.20), respectively. Genotype combinations of the 4 CRP polymorphisms associated with up to a 63% increase in plasma CRP levels (p < 0.001), but not with increased risk of atrial fibrillation. The estimated causal odds ratio for atrial fibrillation by instrumental variable analysis for a doubling in genetically elevated CRP levels was lower than the odds ratio for atrial fibrillation observed for a doubling in plasma CRP on logistic regression (0.94 [95% CI: 0.70 to 1.27] vs. 1.36 [95% CI: 1.30 to 1.44]; p < 0.001).
  
  
  CONCLUSIONS
  Elevated plasma CRP robustly associated with increased risk of atrial fibrillation; however, genetically elevated CRP levels did not. This suggests that elevated plasma CRP per se does not increase atrial fibrillation risk.
authors.affiliation: Department of Clinical Biochemistry, Herlev Hospital, Copenhagen University Hospital, Herlev, Denmark.
authors.forename: Sarah C W
authors.initials: SC
authors.lastname: Marott
authors.forename: Børge G
authors.initials: BG
authors.lastname: Nordestgaard
authors.forename: Jeppe
authors.initials: J
authors.lastname: Zacho
authors.forename: Jens
authors.initials: J
authors.lastname: Friberg
authors.forename: Gorm B
authors.initials: GB
authors.lastname: Jensen
authors.forename: Anne
authors.initials: A
authors.lastname: Tybjaerg-Hansen
authors.forename: Marianne
authors.initials: M
authors.lastname: Benn
mesh_terms: D000328:Adult; D000368:Aged; D001281:Atrial Fibrillation / Q000097:blood / Q000209:etiology*; D002097:C-Reactive Protein / Q000032:analysis* / Q000235:genetics; D003430:Cross-Sectional Studies; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D057182:Mendelian Randomization Analysis; D008875:Middle Aged; D011110:Polymorphism, Genetic; D011446:Prospective Studies
chemical_list: D002097:C-Reactive Protein