Incorporation of covariates into genome scanning using sib-pair analysis in bipolar affective disorder

Assessing heterogeneity in affected relative pair linkage analysis can help control type I error or identify important subgroups. We develop a method to incorporate covariates into sib-pair analysis, and hence are able to test for covariate effects on allele sharing in sib pairs. We propose a way of combining the five bipolar data sets to do a joint analysis of chromosome 18 data using this new method. Our results from a limited set of analyses do not show significant heterogeneity, and do not confirm the linkage previously identified on chromosome 18.