FMR1 and fragile X syndrome: Fragile X syndrome (FXS) is a genetic intellectual disability (ID) in which patients often display autistic features (21–50%) and the fragile X mental retardation 1 (FMR1) gene mutation is the most common monogenic cause of ASD (2–6%) (Budimirovic and Kaufmann, 2011; Mila et al., 2018; Santoro et al., 2012).