Another molecular abnormality found in both human and mouse FXS samples is enhanced signal transduction in the ERK1/2 (extracellular signal-regulated kinases 1 and 2) and PI3K (phosphoinositide 3-kinase) pathways15, 16, 17, 18, 19, which also lead to aberrantly enhanced protein translation through activating S6K1 (ribosomal protein S6 kinase beta-1)20, 21. Here, MAPK3 is linked to fragile X syndrome.