MAPK3 and fragile X syndrome: The Ras-ERK1/2 pathway is of considerable interest in FXS, as inhibitors such as lovastatin and metformin that target this signaling arm correct myriad phenotypes in the Fmr1-KO mouse and rat (Figure 5A) (12, 48, 49), as well as biochemical phenotypes in platelets and neurons derived from patients with FXS (43, 50).