Use of exact and adjusted liability scores to detect genes affecting common traits.

We used the Haseman-Elston sib-pair test to screen for linkage of markers to genes for disease susceptibility in the simulated data as given in Problem 2 of GAW9. We applied the analysis to the underlying quantitative liability trait (Q1), other covariates of Q1 (Q2-Q4), and the dichotomous affection status trait. In addition, we analyzed the residual Q1 after adjusting for the covariates. Using the sib-pair linkage test, we identified a large region of chromosome 5 affecting the residual value of Q1, a region of chromosome 2 affecting Q3, and a region of chromosome 1 possibly affecting Q2. The analysis of the dichotomous traits did not reveal any regions to be significant. This is likely to be due to lack of information since the families were not selected through affected probands.