BackgroundFamily history of asthma and other allergic diseases have been linked to the risk of childhood asthma previously, but little is known about their effect on the age-of-onset and persistency of asthma until young adulthood.MethodsWe assessed the effect of the family history of asthma and allergic diseases on persistent vs. transient, and early- vs. late-onset persistent asthma in The Espoo Cohort Study 1991–2011, a population-based cohort study of 1623 subjects (follow-up rate 63.2%). The determinants were any family history (any parent or sibling); maternal; paternal; siblings only; parents only; and both siblings and parents. Analyses were conducted separately for asthma and allergic diseases while taking the other disease into account as a confounding factor. The outcomes were persistent, transient, early-onset persistent (<13 years) and late-onset persistent asthma. Adjusted risk ratios (RR) were calculated applying Poisson regression. Q-statistics were used to assess heterogeneity between RRs.ResultsFamily history was associated with the different subtypes but the magnitude of effect varied quantitatively. Any family history of asthma was a stronger determinant of persistent (adjusted RR = 2.82, 95% CI 1.99-4.00) than transient asthma (1.65, 1.03-2.65) (heterogeneity: P = 0.07) and on early-onset than late-onset persistent asthma. Also any family history of allergic diseases was a stronger determinant of persistent and early-onset asthma. The impact of paternal asthma continued to young adulthood (early-onset: 3.33, 1.57-7.06 vs. late-onset 2.04, 0.75-5.52) while the influence of maternal asthma decreased with age (Early-onset 3.94, 2.11-7.36 vs. Late-onset 0.88, 0.28-2.81). Paternal allergic diseases did not follow the pattern of paternal asthma, since they showed no association with late-onset asthma. Also the effect estimates for other subtypes were lower than in other hereditary groups (persistent 1.29, 0.75-2.22 vs. transient 1.20, 0.67-2.15 and early-onset 1.86, 0.95-3.64 vs. late-onset 0.64, 0.22-1.80).ConclusionsFamily history of asthma and allergic diseases are strong determinants of asthma, but the magnitude of effect varies according to the hereditary group so that some subtypes have a stronger hereditary component, and others may be more strongly related to environmental exposures. Our results provide useful information for assessing the prognosis of asthma based on a thorough family history.

PURPOSE OF THE STUDY. The goal of this study was to evaluate the risk of a child developing asthma if 1 or both parents has asthma. METHODS. A random sample of 1623 children was followed up over 20 years. The outcome of interest was physiciandiagnosed asthma in parents or children determined by telephone interview at baseline and follow-up surveys. RESULTS. If either of the parents had asthma, the risk of the child developing asthma was significantly increased throughout the study period: the maternal asthma hazard ratio (HR) was 1.91 (95% confidence interval [CI]: 1.36-2.69), and the paternal asthma HR was 2.01 (95% CI: 1.37-2.96). The risk was higher still if both parents had asthma (HR: 3.83 [95% CI: 2.03-7.24]). Siblings conveyed a strong independent risk for the study subject to develop asthma (HR: 2.33 [95% CI: 1.73-3.14]). This risk was even higher when more than one-half of the subject's siblings had asthma, indicating a dose-response pattern (HR: 2.92 [95% CI: 1.94-4.41]). CONCLUSIONS. The results underline the usefulness of asking about asthma in siblings in addition to parental asthma in clinical practice. REVIEWER COMMENTS. We have long known that asthma runs in families. This study helps clarify the risk. If both parents have asthma, the child's risk of developing asthma is greater than if only 1 parent has asthma, and, furthermore, this risk of developing asthma continues into adolescence and young adulthood. Having siblings with asthma also increases the risk even if neither parent has asthma.

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