Fragile-X syndrome (FXS), tuberous sclerosis complex (TSC), and Rett syndrome are among some of the common syndromic ASD which are caused by monogenetic defects, and the corresponding genes that cause FXS (FMR1), TSC (TSC1 and TSC2), and Rett syndrome (MECP2) have been identified [2]. Here, MECP2 is linked to Rett syndrome.