The present invention relates to the identification of genes involved and/or associated with schizophrenia and related diseases, as well as particular identified genes and their potential use in therapy/diagnosis of schizophrenia and related diseases. The genes are all linked to a MAP-kinase signalling chain and are PPMlE; PPMlF,- MAP2K7; MAPK9; RICS/GRIT; PTK2B/PYK2; Gab1; Gab2; Nckl; NckAPI; CrkL; PAKI; CatnKK; CAMK4; MAP4K4; TNIK; MAP3K7; and MAPK8ip1.