Nonetheless, evidence for a direct association between a diagnosis of schizophrenia and COMT variation is mixed: a number of meta-analyses have failed to find any such association (Munafò et al., 2005, Okochi et al., 2009, Taylor, 2018), while others demonstrate a clear association (Costas et al., 2011, González-Castro et al., 2016, Williams et al., 2007). Here, COMT is linked to schizophrenia.