FMR1 and fragile X syndrome: There have been many proposed mechanisms for how loss of Fragile X Mental Retardation Protein (FMRP), the protein encoded by the gene Fmr1, leads to FXS and ASD phenotypes (Bear et al., 2004; Hagerman et al., 2009; Osterweil et al., 2013; Gantois et al., 2017; Rajaratnam et al., 2017, among others).