A final, relevant theme among the significant pathways is the immune system. Antigen processing and presentation pathways from the KEGG and Biocarta databases were significantly enriched for SCZ-associated genes. Although the composition of these pathways was somewhat different between the 2 databases, the core genes of TAP1, TAP2 and HLA-DRA were common to both. The transporter associated with antigen processing (ie, TAP) is composed of a heterodimeric complex of TAP1 and TAP2. It is a key element in the immune recognition of cells compromised by virus infection or malignant transformation. The transporter is crucial in MHC class I antigen presentation by translocating proteasomal degradation products into the lumen of the endoplasmic reticulum for loading onto MHC class I molecules.42 An additional pathway related to the immune system, translocation of ZAP-70 kinase to the immunological synapse, was also significant. The zeta chain–associated protein kinase 70-kDa (ZAP-70) is an integral part of the adaptive immune system because it initiates signaling at the immunological synapse between a T cell and an antigen-presenting cell.43 Previous large-scale genetic studies have implicated the MHC region on
