In support of this theory, there are established cross-sectional associations between schizophrenia and elevations in peripheral pro-inflammatory cytokines, including interleukin-6 (IL-6) and transforming growth factor β (TGF-β).44 Furthermore, elevated plasma levels of inflammatory cytokines early in life increase the risk of the subsequent development of a psychotic illness,45 suggesting that inflammation and psychosis might share a common early developmental aetiology. This evidence concerns the gene TGFB1 and schizophrenia.