The power to detect genetic linkage for quantitative traits in the Utah CEPH pedigrees

Quantitative trait phenotypes and linked marker genotypes were simulated for a range of models with different sets of assumptions based on displacement, prevalence, and heritability of the trait in 30 Utah Centre d'Etude du Polymorphisme Humain (CEPH) families. The gain in power by the addition of 15 families was also estimated by extrapolation. Power was evaluated using both parametric single locus (PSL) models and variance components (VC) methods for two situations: (1) a single marker with 75% heterozygosity and a recombination fraction of 0.05, and (2) a fully informative marker as an approximation to multipoint analysis. When the simulation and analysis models were both dominant with the same prevalence, power greater than or equal to80% for lod >3 was estimated when quantitative trait locus variance was greater than or equal to40% with a displacement of 2.5 or 3. Power was 5-15% lower for recessive models compared to dominant models. With the addition of 15 families, an average increase in power of 17% and 22% was estimated for the dominant and recessive models, respectively. In PSL analyses, power was estimated at less than or equal to20% when the dominance was misspecified. This investigation delineates parameter conditions under which this unique sample affords adequate power to detect linkage using both PSL and VC methods.