FMR1 and fragile X syndrome: Much of our current knowledge on autism spectrum disorder (ASD) is derived from work on animal models of syndromic forms of ASD, which are monogenic disorders caused by mutations in genes including FMR1 (fragile X syndrome), TSC1/TSC2 (tuberous sclerosis), MECP2 (Rett Syndrome), UBE3A (Angelman syndrome), and SHANK3 (Phelan-McDermid syndrome) (reviewed by [1]).