Familial aggregation and segregation analysis of eosinophil levels

The number of circulating eosinophilis is associated with the risk of asthm a in population samples. Therefore, eosinophil levels may be an intermediat e phenotype for asthma amenable to genetic analysis. We examined familiar a ggregation of the number of eosinophils x 10(6) L-1 and the percentage of e osinophils based on a 300 count differential in 644 Hispanic and non-Hispan ic white families, with 2097 subjects, enrolled in the Tucson Children's Re spiratory Study. Both measures were adjusted for age, season and year at th e time blood was drawn, sex, and ethnicity. Segregation analysis was conduc ted in the 458 non-Hispanic white families, as there were no significant fa miliar correlations in the Hispanic families, and there was significant het erogeneity by ethnic group. Familial correlations (p) in the non-Hispanic w hite families were as follows: mother-father, 0.05; mother-child, 0.18 (p < 0.001); father-child, 0.07; sibling-sibling, 0.31 (p < 0.001). Without cov ariates analyses indicated a polygenic/multifactorial mode of inheritance. After adjusting for current and past asthma an oligogenic mode of inheritan ce was suggested, plus additional residual familial components that were ma inly maternally mediated. This study supports the notion of multiple, relat ively common genes interacting to determine genetic susceptibility to asthm a.