MECP2 and fragile X syndrome: Some of the most well-studied monogenic syndromes correlated with ASD in humans are: Fragile X syndrome (FXS) (mutation in FMR1) (Sitzmann et al., 2018), Rett syndrome (RTT) (mutation in MECP2) (Meloni et al., 2000), and tuberous sclerosis (mutations in TSC1 and TSC2) (Bjornsson et al., 1996), which will be analyzed in the next paragraphs.