MAPK3 and fragile X syndrome: For instance, therapeutic testing with metformin and lovastatin, which show promising efficacy in both FXS mouse model19,39 and small scale open-label human studies40,41, is theoretically based on their pharmacological actions against mTORC1 and ERK1/2 (extracellular signal-regulated kinase 1/2), the activity of which is abnormally elevated in FXS mouse model and patients3.