Genome-wide association studies.

Genome-wide association (GWA) studies are best understood as an extension of candidate gene association studies, scaled up to cover hundreds of thousands of markers across the genome in samples usually of several thousand cases and controls. The GWA approach allows the detection of much smaller effect sizes than with previous linkage-based genome-wide studies. However, this sensitivity makes them vulnerable to false positive findings caused by subtle differences between cases and controls that may arise as a result of issues, such as genotyping errors, population stratification, and sample mix-ups as well as the more obvious issue of multiple testing. After some background and an introduction to GWA, studies are considered stage-by-stage with particular focus on quality control as this is by far the most time-consuming and complex issue related to GWA.