[Epidemiological study of genetic and environmental factors in asthma, bronchial hyperresponsiveness and atopy. Protocol and potential selection bias].

BACKGROUND

The EGEA study combines a case-control study and a family study to assess genetic and environmental risk factors and their interactions for asthma, bronchial hyperresponsiveness and atopy. Information is scanty regarding potential selection biases, in particular regarding familial ressemblance 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 (electoral 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 (EGEA II). Potential biases for the various types of analyses have been studied. Quantification of the consequences of the greater participation of probands with a parental history of asthma shows it does not introduce a major bias in the estimates of familial resemblance. Cases and controls showed a good comparability regarding sex, age, area of residence and familial geographical origin, allowing proper associations studies for environmental and candidate genetic factors.

CONCLUSIONS

The case-control component of the study will allow to perform studies on environmental factors and association studies for various genetic polymorphisms. Using the family base collected, segregation and genetic linkage/association analyses with DNA markers may be performed.