FMR1 and atypical Rett syndrome: Significant advancements have been made in identifying molecular mechanisms involved in ASDs by studying disorders with Mendelian inheritance patterns such as Tuberous Sclerosis complex (TSC1 and TSC2), Rett syndrome (MECP2), Fragile X syndrome (FXS; which results from mutated Fragile X mental retardation-1, FMR1), and Cowden syndrome (PTEN), but, altogether, these disorders do not account for more than 10% of cases [4].