title: Helicobacter pylori infection: genetic and environmental influences. A study of twins.
abstract: OBJECTIVE
  To investigate the importance of genetic effects for acquiring Helicobacter pylori infection.
  
  
  METHODS
  Cross-sectional study on monozygotic and dizygotic twins, reared apart and reared together.
  
  
  METHODS
  Twins from a subregistry of the Swedish Twin Registry, which includes entries for about 25,000 twin pairs who were born in Sweden.
  
  
  METHODS
  Helicobacter pylori status was assessed as the presence of anti-H. pylori IgG in 269 pairs of twins, including 36 monozygotic twin pairs reared apart, 64 monozygotic twin pairs reared together, 88 dizygotic twin pairs reared apart, and 81 dizygotic twin pairs reared together.
  
  
  RESULTS
  The probandwise concordance rate for H. pylori infection was higher in monozygotic twin pairs (81%) than in dizygotic twin pairs (63%) (P = 0.001). Probandwise concordance rates for H. pylori infection among 124 pairs of twins reared apart were 82% and 66% for monozygotic and dizygotic twins, respectively (P = 0.003). The correlation coefficient was 0.66 for monozygotic twins reared apart, and it provides the best single estimate of the relative importance of genetic effects (heritability) for variation in the acquisition of H. pylori infection. The heritability estimate from model-fitting analyses was 0.57, a similar result. The remaining variance was accounted for by shared rearing environmental (20%) and nonshared environmental factors (23%). The latter contribute to differences, not similarities, among family members.
  
  
  CONCLUSIONS
  This twin study showed that genetic effects influence the acquisition of H. pylori infection because of greater similarities within the monozygotic twin pairs. Further, sharing the same rearing environment also contributes to the familial tendency for acquiring H. pylori infection.
authors.affiliation: Veterans Affairs Medical Center, Houston, Texas.
authors.forename: H M
authors.initials: HM
authors.lastname: Malaty
authors.forename: L
authors.initials: L
authors.lastname: Engstrand
authors.forename: N L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: D Y
authors.initials: DY
authors.lastname: Graham
mesh_terms: D016009:Chi-Square Distribution; D002648:Child; D002668:Child Rearing; D003430:Cross-Sectional Studies; D004200:Diseases in Twins; D020022:Genetic Predisposition to Disease; D016481:Helicobacter Infections / Q000235:genetics*; D016480:Helicobacter pylori; D006801:Humans; D008875:Middle Aged; D012931:Social Environment; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic