Increased levels of MMP-9 have been demonstrated in human subjects with FXS (Dziembowska et al., 2013; Sidhu et al., 2014), ASD (Abdallah et al., 2012), bi-polar disorder (Rybakowski et al., 2013) and treatment-resistant schizophrenia (Yamamori et al., 2013). Here, MMP9 is linked to schizophrenia.