Epidemiological study of the Genetics and Environment of Asthma, bronchialhyperresponsiveness and atopy (EGEA). Protocol and potential selection factors

Background: The EGEA study combines a case-control study and a family study to assess genetic and environmental risk factors and their interactions fo r asthma, bronchial hyperresponsiveness and atopy. Information is scanty re garding potential selection biases, in particular regarding familial ressem blance in epidemiological surveys of this kind. Methods : Asthmatic probands (adult and paediatric) were recruited in chest clinics of six clinical centres. Controls were mostly population-based (el ectoral rolls) for adults and recruited in surgery departments for children . Results: The population examined includes 348 nuclear families ascertained by one asthmatic and 416 controls, totalling 1847 subjects (EGEA I) and an additional sample of 40 families ascertained by two asthmatic siblings (EGE A II). Potential biases for the various types of analyses have been studied . Quantification of the consequences of the greater participation of proban ds with a parental history of asthma shows it does not introduce a major bi as in the estimates of familial resemblance. Cases and controls showed a go od comparability regarding sex, age, area of residence and familial geograp hical origin, allowing proper associations studies for environmental and ca ndidate genetic factors. Conclusions: The case-control component of the study will allow to perform studies on environmental factors and association studies for various geneti c polymorphisms. Using the family base collected, segregation and genetic l inkage/association analyses with DNA markers may be performed.