Formation of Chimeric Genes by Copy Number Variation as a Mutational Mechanism in Schizophrenia

Abstract

Chimeric genes are caused by structural genomic rearrangements that fuse together portions of two different genes to create a novel gene. Chimeras may differ from their parent genes in localization, regulation, or function. We screened 122 individuals with schizophrenia and 120 controls for germline rearrangements anywhere in the genome leading to chimeras. Three cases and zero controls harbored such events: fusions of MATK to ZFR2, of DNAJA2 to NETO2, and of MAP3K3 to DDX42. Each fusion produces a stable protein when exogenously expressed in cultured cells. Temporal expression data indicate that the parent genes of all three chimeras are expressed in the brain during development. We detected the chimeric transcripts of DNAJA2-NETO2 and MAP3K3-DDX42 in patient lymphoblasts; parent genes of the MATK-ZFR2 chimera are expressed only in the brain. Formation of chimeras involved loss of critical domains of parent genes. Subcellular localizations of DNAJA2-NETO2 and MAP3K3-DDX42 are dramatically altered compared to their parent genes. The MATK-ZFR2 chimera includes a novel, frame-shifting splice variant of the previously uncharacterized ZFR2 gene. In contrast with the nuclear localization of full-length ZFR2, frameshifted ZFR2 localizes preferentially to dendritic branch sites, and its chimera is predicted to be highly overexpressed during development. Germline chimeric mutations in schizophrenia provide a new model for functional interpretation of structural variation in human illness, and implicate new genes and pathways in schizophrenia pathogenesis.