title: Heterogeneity in IBD allele sharing among covariate-defined subgroups: issues and findings for affected relatives.
abstract: OBJECTIVE
  Modelling of variation in identical-by-descent (IBD) allele sharing using covariates can increase power to detect linkage, identify covariate-defined subgroups linked to particular marker regions, and improve the design of subsequent studies to localize genes and characterize their effects. In this report, we highlight issues that arise in studies of families with affected relatives.
  
  
  METHODS
  Mirea et al. [Genet Epidemiol 2003, in press] extended linear and exponential linkage likelihood models [Kong and Cox, Am J Hum Genet 1997;61: 1179-1188] to model variation in NPL scores among covariate-defined groups of families, and proposed likelihood ratio (LR) and t statistics to detect differences in allele sharing between groups defined by a binary covariate. Here we evaluate factors affecting the power of these tests analytically and by example, as well as effects of constraints, nuisance parameters, and incomplete data on test validity by simulation of locus heterogeneity in families with affected siblings or affected cousins.
  
  
  RESULTS
  Provided constraints on the parameters are avoided, these tests are particularly useful when one subgroup has less than expected IBD sharing. The distribution of the LR statistic depends on the extent of linkage, particularly in the presence of constraints. The t statistic may be biased by group differences in information content.
  
  
  CONCLUSIONS
  We recommend that constraints be applied cautiously, and covariate effects in IBD allele sharing models interpreted with care.
authors: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ont., Canada. bull@mshri.on.ca
authors: Shelley B
authors: SB
authors: Bull
authors: Lucia
authors: L
authors: Mirea
authors: Laurent
authors: L
authors: Briollais
authors: Alexander G
authors: AG
authors: Logan
mesh_terms: D000483:Alleles; D000704:Analysis of Variance; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D005808:Genes, Recessive; D018740:Genetic Heterogeneity; D008040:Genetic Linkage; D020022:Genetic Predisposition to Disease; D006801:Humans; D006973:Hypertension / Q000235:genetics