FMR1 and Rett syndrome: Many common syndromic disorders with a significant ASD component are caused by alterations in genes that directly or indirectly participate in the mammalian target of rapamycin (mTOR) signaling pathway, i.e., tuberous sclerosis (TSC1/2), fragile X mental retardation 1 (FMR1), neurofibromatosis type 1 (NF1), PTEN mutation syndrome, and Rett’s syndrome (MECP2; reviewed in Levitt and Campbell, 2009).