title: Missing heritability in the tails of quantitative traits? A simulation study on the impact of slightly altered true genetic models.
abstract: OBJECTIVE
  Genome-wide association studies have identified robust associations between single nucleotide polymorphisms and complex traits. As the proportion of phenotypic variance explained is still limited for most of the traits, larger and larger meta-analyses are being conducted to detect additional associations. Here we investigate the impact of the study design and the underlying assumption about the true genetic effect in a bimodal mixture situation on the power to detect associations.
  
  
  METHODS
  We performed simulations of quantitative phenotypes analysed by standard linear regression and dichotomized case-control data sets from the extremes of the quantitative trait analysed by standard logistic regression.
  
  
  RESULTS
  Using linear regression, markers with an effect in the extremes of the traits were almost undetectable, whereas analysing extremes by case-control design had superior power even for much smaller sample sizes. Two real data examples are provided to support our theoretical findings and to explore our mixture and parameter assumption.
  
  
  CONCLUSIONS
  Our findings support the idea to re-analyse the available meta-analysis data sets to detect new loci in the extremes. Moreover, our investigation offers an explanation for discrepant findings when analysing quantitative traits in the general population and in the extremes.
authors: Institute for Medical Informatics, Biometry and Epidemiology, University of Duisburg-Essen, Essen, Germany.
authors: Carolin
authors: C
authors: Pütter
authors: Sonali
authors: S
authors: Pechlivanis
authors: Markus M
authors: MM
authors: Nöthen
authors: Karl-Heinz
authors: KH
authors: Jöckel
authors: Heinz-Erich
authors: HE
authors: Wichmann
authors: André
authors: A
authors: Scherag
mesh_terms: D015992:Body Mass Index; D016022:Case-Control Studies; D003198:Computer Simulation; D055106:Genome-Wide Association Study; D005838:Genotype; D006801:Humans; D040582:Inheritance Patterns / Q000235:genetics*; D008957:Models, Genetic; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D019655:Quantitative Trait, Heritable