SYNGAP1 and fragile X syndrome: Two notable examples of this are fragile X syndrome (FXS) and SYNGAP1-related intellectual disability (SRID), which arise from mutations in FMR1 and SYNGAP1, respectively (Qin et al., 2005; Dolen et al., 2007; Osterweil et al., 2010; Wang et al., 2013; Barnes et al., 2015).