Are genetic influences on peptic ulcer dependent or independent of geneticinfluences for Helicobacter pylori infection?

Background: Genetic factors play a role or roles in the etiology of peptic ulcer disease and the acquisition of Helicobacter cobacter pylori infection . Objective: To evaluate the relative importance of genetic and environmental influences as well as the importance of H pylori on peptic ulcer disease. Design: Cross-sectional study on monozygotic (iMZ) and dizygotic (DZ) twins , reared apart or together. Participants: Twins of the subregistry of the Swedish Twin Registry include d in the Swedish Adoption/Twin Study of Aging. Measurements: Peptic ulcer disease and H pylori status were assessed in MZ and DZ twin pairs reared apart or together. A total of 258 twin pairs had i nformation regarding H pylori status and history of peptic ulcer. Helicobac ter pylori status was assessed as the presence of anti-H pylori IgG. Results: The intraclass correlations for peptic ulcer disease for MZ twins reared apart and together and DZ twins reared apart and together were 0.67, 0.65, 0.22, and 0.35, respectively, which indicates that genetic effects a re important for liability to peptic ulcer. The correlation coefficient for MZ twins reared apart (0.67) provides the best single estimate of the rela tive importance of genetic effects (heritability) for variation in liabilit y to peptic ulcer disease, and structural model fitting analyses confirmed this result (heritability, 62%). The cross-twin cross-trait correlations fo r MZ and DZ twins were examined to determine whether genetic effects for pe ptic ulcer were shared with or independent of genetic influences for H H py lori The cross-correlations for MZ and DZ twins were almost identical (0.25 and 0.29, respectively), suggesting that familial environmental rather tha n genetic influences mediate the association between peptic ulcer disease a nd H pylori infection. Conclusions: Genetic influences are of moderate importance for liability to peptic ulcer disease. Genetic influences for peptic ulcer are independent of genetic influences important for acquiring H pylori infection.