title: Testing genetic linkage with relative pairs and covariates by quasi-likelihood score statistics.
abstract: OBJECTIVE
  Genetic linkage analysis of common diseases is complicated by the heterogeneity of genetic and environmental factors that increase disease risk, and possibly interactions among them. Most linkage methods that account for covariates are restricted to sib pairs, with the exception of the conditional logistic regression model [1] implemented in LODPAL in the S.A.G.E. software [2]. Although this model can be applied to arbitrary pedigrees, at times it can be difficult to maximize the likelihood due to model constraints, and it does not account for the dependence among the different types of relative pairs in a pedigree.
  
  
  METHODS
  To overcome these limitations, we developed a new approach based on score statistics for quasi- likelihoods, implemented as weighted least squares. Our methods can be used to test three different hypotheses: (1) a test for linkage without covariates; (2) a test for linkage with covariates, and (3) a test for effects of covariates on identity by descent sharing (i.e., heterogeneity). Furthermore, our methods are robust because they account for the dependence among different relative pairs within a pedigree.
  
  
  CONCLUSIONS
  Although application of our methods to a prostate cancer linkage study did not find any critical covariates in our data, the results illustrate the utility and interpretation of our methods, and suggest, nonetheless, that our methods will be useful for a broad range of genetic linkage heterogeneity analyses.
authors.affiliation: Division of Biostatistics, Department of Health Sciences Research, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. schaid@mayo.edu
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Schaid
authors.forename: Jason P
authors.initials: JP
authors.lastname: Sinnwell
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Thibodeau
mesh_terms: D005260:Female; D018740:Genetic Heterogeneity; D008040:Genetic Linkage; D020022:Genetic Predisposition to Disease; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008957:Models, Genetic; D010375:Pedigree; D011471:Prostatic Neoplasms / Q000235:genetics