Early respiratory infections: the role of passive smoking in gene-environment interaction.

This study aims to: (i) estimate genetic and environmental components of four early respiratory diseases and (ii) test if these components are modified by parental smoking exposure. Study subjects were 2068 Italian twins aged 3-17. We performed biometric modeling under the assumptions of the twin design. For bronchitis and bronchiolitis, variance was mostly explained by shared environment, with no modification effect by parental smoking. For pneumonia and wheezy bronchitis, shared environmental component was larger among passive smokers, while genetic component was predominant among non-smokers. In the etiology of pneumonia and wheezy bronchitis, parental smoking could be a major familial factor.