Increased concordance of severe respiratory syncytial virus infection in identical twins

OBJECTIVE: We estimated differences in the severity of respiratory syncytial virus infection attributable to genetic and environmental factors. METHODS: Record linkage data on hospitalizations attributable to respiratory syncytial virus infection were gathered on all twins (12,346 pairs) born in Denmark between 1994 and 2003. Latent-factor models of genetic and environmental effects were fitted to the observed data by using maximal likelihood methods. RESULTS: Identical twins resembled each other significantly more than did fraternal twins for respiratory syncytial virus hospitalization (concordance rate: 0.66 vs 0.53), which suggests genetic influences on disease severity. Genetic factors accounted for 16%, family environment for 73%, and nonshared environment for 11% of the individual susceptibility to develop severe respiratory syncytial virus infection. CONCLUSIONS: The severity of respiratory syncytial virus infection is determined partly by genetic factors. This result should stimulate the search for genetic markers of disease severity.