Familial aggregation and heritability of pyloric stenosis.

CONTEXT Pyloric stenosis is the most common condition requiring surgery in the first months of life. Case reports have suggested familial aggregation, but to what extent this is caused by common environment or inheritance is unknown. OBJECTIVES To investigate familial aggregation of pyloric stenosis from monozygotic twins to fourth-generation relatives according to sex and maternal and paternal contributions and to estimate disease heritability. DESIGN, SETTING, AND PATIENTS Population-based cohort study of 1,999,738 children born in Denmark between 1977 and 2008 and followed up for the first year of life, during which 3362 children had surgery for pyloric stenosis. MAIN OUTCOME MEASURE Familial aggregation of pyloric stenosis, evaluated by rate ratios. RESULTS The incidence rate (per 1000 person-years) of pyloric stenosis in the first year of life was 1.8 for singletons and 3.1 for twins. The rate ratios of pyloric stenosis were 182 (95% confidence interval [CI], 70.7-467) for monozygotic twins, 29.4 (95% CI, 9.45-91.5) for dizygotic twins, 18.5 (95% CI, 13.7-25.1) for siblings, 4.99 (95% CI, 2.59-9.65) for half-siblings, 3.06 (95% CI, 2.10-4.44) for cousins, and 1.60 (95% CI, 0.51-4.99) for half-cousins. We found no difference in rate ratios for maternal and paternal relatives of children with pyloric stenosis and no difference according to sex of cohort member or sex of relative. The heritability of pyloric stenosis was 87%. CONCLUSION Pyloric stenosis in Danish children shows strong familial aggregation and heritability.