[Significance of genetic and environmental factors for asthma. A population-based study of 11.688 Danish twin pairs].

The aim of this study was to estimate the relative influence of genetic and environmental factors on the aetiology of asthma. The classic twin study design was used to analyse data on self-reported asthma obtained by a questionnaire mailed to 34,076 individuals, aged 12-41 yrs and originating from the Danish Twin Register. The cumulative incidence proportion was 6.2% in the pooled sample. No overall sex or zygosity difference was observed. Substantially higher concordance rate, odds ratio and correlation for asthma were estimated in monozygotic than dizygotic twin pairs. Using biometric modelling, a model including additive genetic and non-shared environmental effects provided the best fit to the data. According to this model, 73% of the variation in liability to asthma was explained by genetic effects. The results emphasize a major genetic component in the aetiology of asthma.