These data are consistent with previous studies (Wang et al, 2008; Wilczynski et al, 2008; Szepesi et al, 2013, 2014; Vafadari et al, 2016), arguing that higher MMP‐9 levels could confer higher spine plasticity in the MMP‐9_T variant, similar to the greater abundance of thin spines and higher MMP‐9 activity that are observed in FXS patients and Fmr1 knockout mice (Rudelli et al, 1985; Comery et al, 1997; Dziembowska et al, 2013). Here, MMP9 is linked to fragile X syndrome.