Genetic and environmental influences on the risk of acute appendicitis in twins

Background: Acute appendicitis is common but the aetiology is unclear. This study examined the heritability of acute appendicitis. Methods: The study included twin pairs with known zygosity burn between 1959 and 1985. Individuals with acute appendicitis were found by record linkage with the Swedish Inpatient Register. Comparing monodizygotic and dizygotic twins, the similarity and relative proportions of phenotypic variance resulting from genetic and environmental factors were analysed. Risks of acute appendicitis explained by heritability and environmental effects were estimated. Results: Some 3441 monozygotic and 2429 dizygotic twins were identified. Almost no genetic effects were found in males (8 (95 per cent confidence interval 0 to 50) per cent), but shared (31 (0 to 49) per cent) and non-shared (61 (47 to 74) per cent) environmental factors accounted for this risk. In females, the heritability was estimated as 20 (0 to 36) per cent and the remaining variation was clue to non-shared environmental factors (80 (64 to 98.) per cent). For the sexes combined, genetic effects accounted for 30 (5 to 40) per cent and non-shared environmental effects for 70 (60 to 81) per cent of the risk. Conclusion: Acute appendicitis has a complex aetiology with sex differences in heritability and environmental factors.