FMR1 and fragile X syndrome: Interestingly, aberrations in dendritic spines that are observed in FXS patients (Rudelli et al, 1985) and Fmr1 knockout mice (Comery et al, 1997) have been linked to elevated synaptic levels of MMP‐9 (Bilousova et al, 2009; Dziembowska et al, 2013; Gkogkas et al, 2014; Sidhu et al, 2014).