The molecular signaling pathways involved in fragile X (e.g., phosphoinositide 3-kinase or PI3-kinase and mammalian target of rapamycin or mTOR) lay at the confluence of molecular signaling pathways underlying several other genetically defined autistic syndromes (e.g., Rett Syndrome, PTEN, and tuberous sclerosis) and have been implicated in Parkinson’s disease [56–58]. This evidence concerns the gene PTEN and atypical Rett syndrome.