Covariates in linkage analysis

We apply a novel technique to detect significant covariates in linkage anal ysis using a logistic regression approach. An overall test of linkage is fi rst performed to determine whether there is significant perturbation from t he expected 50% sharing under the hypothesis of no linkage; if the overall test is significant, the importance of the individual covariate is assessed . In addition, association analyses were performed. These methods were appl ied to simulated data from multiple populations, and detected correct marke r linkages and associations. No population heterogeneity was detected. Thes e methods have the advantages of using all sib pairs and of providing a for mal test for heterogeneity across populations. (C) 1999 Wiley-Liss, Inc.