EDITORIAL Genetic and environment in asthma: the answer of twin studies

Twin studies have been widely used to estimate the genetic contribution to diseases. In this issue of the Euro-pean Respiratory Journal, SKADHAUGE et al. [1] present the results of a large Danish population-based twin study on asthma. In this study, the heritability in liability to asth-ma, i.e. the proportion of variance due to genetic factors, is estimated to be 0.77 for males and 0.68 for females. In other studies, the heritability of asthma is estimated to be between 0.36 and 0.75 [2–4] (table 1). Thus, the results of this Danish study are consistent with those of other twin studies and add to the body of evidence indicating that the genetic contribution to asthma is considerable. In addition, the results of this study suggest individual specific, un-shared, environmental factors to be important as well. In this editorial, the assumptions and methods of twin stu