Extracellular matrix metalloproteinase 9 (MMP-9) regulates spine morphology, synaptic plasticity, learning and memory (Huntley, 2012), and is implicated in phenotypes in rodent models of ASD and FXS (Bilousova et al., 2009; Rotschafer et al., 2012; Dziembowska et al., 2013; Sidhu et al., 2014). This evidence concerns the gene MMP9 and fragile X syndrome.