Bronchial asthma is the most common chronic disease affecting children and young adults. It is a complex genetic disorder with a heterogeneous phenotype, largely attributed to the interactions among many genes and between these genes and the environment. Asthma-related traits include clinical symptoms of asthma, such as coughing, wheezing, and dyspnea; bronchial hyperresponsiveness (BHR) as assessed by methacholine challenge test; serum IgE levels; atopy; and atopic dermatitis (Laitinen et al., 2001; Illig and Wjst, 2002; Pillai et al., 2006). See 147050 for information on the asthma-associated phenotype atopy.