While Fragile X syndrome itself is separate from autism, it is the leading monogenic cause of autism, as a significant proportion of individuals with FXS also meet the clinical diagnostic criteria for ASD (Feinstein and Reiss, 1998) and mutations in FMR1 are present in up to 5 percent of ASD cases (Reddy, 2005). The gene discussed is FMR1; the disease is autism.