In some patients with FXS, lack of FMRP may affect serotonin-mediated pathways (Hanson and Hagerman, 2014; Protic et al., 2019) and serotonin receptor agonists and selective serotonin reuptake inhibitors have been shown to ameliorate behavioral deficits in the Fmr1 KO mouse (Uutela et al., 2014; Costa et al., 2018; Tao et al., 2023; Kim et al., 2022). This evidence concerns the gene FMR1 and fragile X syndrome.