The genetic basis of atopic asthma.

Asthma is a respiratory disease characterized by recurrentrespiratory symptoms, reversible variable airway obstruction,airway inflammation and increased airway responsiveness. Atopy is a disorder involving immunoglobulin E(IgE) antibody responses to ubiquitous allergens, and iscommonly associated with asthma. Because of its complexclinical phenotype, the genetic basis of asthma can bestudied using intermediate or surrogate phenotypes thatcan be measured objectively, such as the presence ofatopy or bronchial hyperresponsiveness (BHR), althoughthese are not specific to asthma. Furthermore, despite theclose relationship between atopy, bronchial hyperresponsivenessand asthma, they are not interchangeable:most asthmatics are atopic, but atopic subjects may not havebronchial hyperresponsiveness or asthma symptoms andsubjects with bronchial hyperresponsiveness may not beatopic or asthmatic. The phenotype can bedefined in several ways ranging from subjective measures(e.g. symptoms), objective measures (e.g. BHR or serumIgE level) or both. It is this lack of a clear definition ofasthmatic phenotypes that presents the biggest problemwhen reviewing studies of the genetic basis of asthma andatopy, with multiple definitions of the same intermediatephenotype being used in different studies.