Factors influencing the prevalence of asthma among first degree relatives of extrinsic and intrinsic asthmatics.

The prevalence of asthma, hay fever, and eczema was examined in first degree relatives of extrinsic (atopic) and intrinsic (non-atopic) asthmatics attending the asthma clinics of the Brompton Hospital and the Doncaster Royal Infirmary. In both the Doncaster and Brompton populations the prevalence of asthma, hay fever, and eczema was significantly higher among relatives of extrinsic than among relatives of intrinsic asthmatics. Furthermore, the prevalence of these traits tended to be higher among siblings of extrinsic probands with one or both parents affected than among siblings of probands with neither parent affected. Most importantly, the prevalence of asthma among first degree relatives was positively correlated with the prevalence of hay fever or eczema or both among relatives and with the degree of atopy in the probands. These findings are consistent with the results of previous investigations in which the expression of asthma was shown to depend on a genetic predisposition to the trait as well as exposure to environmental provoking agents. We further suggest that the presence of atopy in genetically predisposed individuals increases the risk of developing asthma.