PTEN and fragile X syndrome: The mTOR signaling pathway is a convergent pathway that is disturbed by genetic variations in the TSC1 and TSC2 (TSC), PTEN (Bannayan-Riley-Ruvalcaba syndrome, Lhermite-Duclos syndrome, and Cowden syndrome), FMRP (fragile X syndrome), and NF1 (neurofibromatosis type 1) genes.