Respiratory Syncytial Virus and Asthma in Twin Children: Lessons from the Population-Based Danish Registries

Several hypotheses have been proposed regarding the association between RSV infection and asthma but the true nature of their relationship has remained ambiguous. Particularly, it is not clear whether the RSV infection plays a direct causative role in asthma or simply identifies infants at risk for subsequent wheezing resulting from an asthmatic predisposition or pre-existing abnormal lung function. An alternative explanation suggests that severe RSV infection and asthma arise from shared genetic and/or environmental determinants. We review the literature on the relationship between RSV infection and asthma in twins with special emphasis on the population-based twin studies from Denmark. The Danish Twin Registry is one of the oldest and most well-structured twin registries in the world and we show that combining elaborate registry information with paraclinical and clinical data can be used to elucidate how environmental factors interact with the genetics in the development of severe RSV infection and asthma. We conclude that severe infant RSV infection does not seem to cause asthma but rather is an indicator of the genetic predisposition to asthma.