MMP9 and fragile X syndrome: Interestingly, it has been shown that the circulating level of MMP9 (Matrix Metalloproteinase 9), Ras, Hk1 (Hexokinase 1), APP (amyloid-β precursor protein) and ERK (Extracellular Regulated Kinase) phosphorylation in blood platelets can be modulated following specific treatment, thus corroborating their potential use as objective outcome measures for FXS clinical trials11,12,14,16.