PTEN and fragile X syndrome: Furthermore, in addition to the genetic defect in Tsc1/2 and Pten, the lack of FMR1 expression, which leads to fragile X syndrome (FXS), an autism-associated disorder, also demonstrated hyperactive mTOR signaling both in KO mice and in FXS patients (Sharma et al., 2010; Hoeffer et al., 2012).