The first GWA study of schizophrenia based on individual genotyping used a sample of only 178 cases and 144 controls (Lencz et al., 2007). The best hit was a variant in the vicinity of the colony-stimulating factor-2 receptor alpha (CSF2RA) gene, but this did not reach genome-wide significance (Lencz et al., 2007). The second GWA study based on individual genotyping included a larger sample of 738 patients and 733 controls. This study also failed to find any genome-wide significant association, although a few signals coincided with genomic regions implicated previously in schizophrenia (Sullivan et al., 2008). O'Donovan et al. (2008) performed their initial GWA study using a moderately sized sample of 479 patients. However, they enhanced the statistical power by conducting a follow-up study of 12 markers associated with a p-value ≤10−5 in a much larger sample. Three of these 12 markers showed strong evidence for replication (p ≤ 5 × 10−4). However, their best supported variant failed to achieve the level of genome-wide significance (Table 1). The highest ranking SNP from this study is located in an intron of
