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Background: In case-control studies of Europeans, hetero-zygosity for Arg702Trp(rs2066844), Gly908Arg(rs2066845) and Leu1007fsinsC(rs5743293) on the NOD2/CARD15 gene is associated with a 2-fold greater risk of Crohn disease, whereas homozygosity or compound heterozygosity is associated with a 17-fold greater risk. However, the importance of these genetic variants if identified in particular individ - uals within the general population is unknown. We undertook this study to estimate the penetrance of these variants in the general population. Methods: We genotyped 43 596 individuals from the Danish general population followed between January 1976 and July 2007. Using a logistic regression model, we estimated the risk of Crohn disease in relation to variants of the NOD2/CARD15 gene in the general population. Penetrance was calculated as the fraction of participants in whom Crohn disease was diagnosed before age 50 years. Results: In the general population, 89% of participants were noncarriers of the genetic variants of interest (n = 38 594), 11% were heterozygotes (n = 4838), and 0.4% were compound heterozygtes or homozygotes (n = 164). For Crohn disease, multifactorially adjusted odds ratios were 1.2 (95% confidence interval [CI] 0.8-1.9) for heterozygotes and 3.3 (95% CI 0.8-13.6) for compound heterozygotes and homozygotes combined, relative to noncarriers. Only 2 compound heterozygotes received a diagnosis of Crohn disease, and this disease was not diagnosed in any of the homo - zygotes. The penetrance at age 50 years of NOD2/CARD15 genetic variants of Crohn disease was 0.30% (95% CI 0.29%-0.31%) for heterozygotes and 1.5% (95% CI 1.4%- 1.6%) for compound heterzygotes and homozygotes. Interpretation: The penetrance of NOD2/CARD15 genetic variants in relation to risk of Crohn disease for this Danish population was lower than might have been expected from previous European case-control studies. This should be considered when advising healthy individuals in whom these genetic variants are identified. [ABSTRACT FROM AUTHOR]