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Infants with severe respiratory syncytial virus (RSV) infection are at increased risk for asthma (JW Gen Med Sep 10 1999). Recent data suggest the possibility of a common genetic source for the two diseases. To examine this possibility, researchers gathered data on twins born alive in Denmark between 1994 and 2000 who had been hospitalized for RSV infection and compared this information with two measures for asthma.
A total of 5154 twin-pairs, including both monozygotic and dizygotic twins, had complete data and were studied. Several phenotypic models were constructed to compare covariance based on genetics, using observed incidences of RSV hospitalization and asthma for the twins and factoring in common environmental effects as well as unique environmental factors. In a bivariate Cholesky model, shared genetic effects were found to underlie all of the covariance between RSV hospitalization and asthma. Moreover, the fit of a direction-of-causation model did not worsen when asthma was assumed to cause severe RSV (P=0.39), but it deteriorated significantly when severe RSV was assumed to cause asthma (P<0.001).
Thomsen SF et al. Exploring the association between severe respiratory syncytial virus infection and asthma: A registry-based twin study. Am J Respir Crit Care Med 2009 Jun 15; 179:1091.
Comment
This study involved the use of very complex models, making interpretation by a nonexpert difficult. Nonetheless, its results strongly suggest the presence of an underlying genetic link between early severe RSV infection and asthma. It also disproves the idea that RSV infection severe enough to require hospitalization leads to childhood asthma.