Combined multipoint analysis of multiple asthma data sets based on the posterior probability of linkage

In the presence of multiple data sets, an important issue is how to best measure the overall evidence for linkage across data sets. Previously, we advocated the use of the posterior probability of linkage (PPL) for this purpose [Vieland, Am J Hum Genet 63:947-54, 1998; Wang et al., Ann Hum Genet 64:533-53, 2000; Vieland et al., Hum Hered 51:199-208, 2001]. In this paper, we propose a critical modification of our earlier two-point PPL in order to handle multiple-point calculations. The proposed modification is then applied to the genome-screen data sets and the COAG chromosome 5 data sets provided by GAW 12. We find linkage signals at location (in the order of the strength of the signal) 45 cM on chromosome 6, 23 cM on chromosome 20, and 30 cM on chromosome 1. No linkage signal is found on chromosome 5.