In fact, the largest schizophrenia GWAS to date found SNPs in three genes (CACNA1C, ITPR3 and CYP2D6) within the serotonergic synapse pathway reached GWAS significance (P<5 × 10−8) and SNPs in another 17 genes within this pathway were nominally significant (P<1 × 10−5).2 Furthermore, a recent gene-set enrichment analysis of the SZGene database25 identified 24 pathways significantly enriched for schizophrenia candidate genes among which the serotonin receptor signaling pathway was ranked second.7 This evidence concerns the gene CYP2D6 and schizophrenia.