Scores of asthma and asthma severity reveal new regions of linkage in EGEA study families

There is ongoing debate as to how asthma should be defined in order to forward understanding of the underlying mechanisms. The aim of the present study was to build quantitative scores of asthma and asthma severity and to assess whether refinement of disease phenotypes can facilitate the identification of chromosomal regions harbouring susceptibility genes. A genome-wide linkage scan was conducted in 110 families with at least two asthmatic siblings (n=508) from the French Epidemiological study on the Genetics and Environment of Asthma, bronchial hyperresponsiveness and atopy (EGEA). The phenotypes studied were an asthma severity score (assessed among asthmatics by combining clinical data and treatment), forced expiratory volume in one second (FEV1) and an asthma score (including both asthmatics and nonasthmatics and representing the whole disease spectrum). This analysis showed genome-wide suggestive evidence of linkage of the asthma score to 18p11, a novel region undetected in a previous screen of dichotomous asthma. There was potential linkage of 2p23 to asthma severity score and of three regions (1p36, 2q36 and 6q14) to FEV1. Moreover, FEV1 appeared to have no genetic determinant in common with asthma severity and asthma scores. Asthma and asthma severity quantitative scores revealed new regions of linkage and thus provide support for considering these phenotypes in future genetic studies.