Common variant effects may be detected using a GWAS, which tests such effects at markers spaced across the entire genome. Current platforms for GWAS include thousands to millions of individual single-nucleotide polymorphism markers. Each marker is tested for variant frequency differences between cases and controls. Such analyses must be corrected for multiple testing. The currently accepted significance threshold for GWAS is 5 × 10−8, and this threshold is generally reached only by using very large sample sizes. A recent schizophrenia GWAS1 included more than 30,000 cases and resulted in the identification of more than 100 independent genetic loci, which are now being analyzed for clues to pathophysiology.
