Furthermore, several single-gene mutation syndromic disorders incur increased risk of developing ASD including Rett syndrome (MeCP2), Fragile X (FMR1), Tuberous sclerosis (either TSC1 or TSC2), Cowden syndrome (PTEN), Timothy syndrome (CACNA1C), and Angelman syndrome (UBE3A) (17–19). Here, FMR1 is linked to Down syndrome.