Factor analysis of asthma and atopy traits shows 2 major components, one of which is linked to markers on chromosome 5q

Background: A variety of definitions of asthma and atopy traits have been u sed in genetic studies. The variables used may be correlated, increasing th e likelihood of type I error. Objective: We sought to clarify and quantify phenotypes that may be charact erized by related traits. Principal components and factor analysis were app lied to the correlation matrix of asthma and atopy traits before linkage an alysis. Methods: Factor analysis was performed on 468 Hispanic and non-Hispanic whi te children enrolled in the Tucson Children's Respiratory Study, with compl ete information on 24 items, including skin test response to 7 allergens, t otal serum IgE levels, presence or absence of asthma attacks, wheezing epis odes, hay fever, and cough. Factor score coefficients were then applied to all siblings (n = 877), and quantitative factor scores were derived. Single -point and multipoint nonparametric sib-pair analyses were performed to ass ess linkage to markers on chromosome 5q31-33. Analyses were also performed for individual items. Results: Two main factors were identified: Factor I had high loadings on at opic items, including skin test responses, IgE, and hay fever, and Factor I I had high loadings that included asthma diagnosis, wheezing, cough, and Al ternaria species skin test response. Factors I and II were correlated at an r value of 0.19. For the quantitative factor scores, significant single-po int linkage (P <.0001) was demonstrated only for atopic Factor I, and a pea k multipoint LOD score of 2.7 was seen for marker D5S479. Multipoint LOD sc ores for individual items were 1.1 or less. Conclusion: These analyses suggest evidence for a locus or loci mapping to chromosome 5q31-33 associated with this composite atopic phenotype.