FMR1 and fragile X syndrome: Interestingly, profilin1 acts downstream of the fragile X mental retardation protein state FMRP in neural progenitors (Saffary and Xie, 2011) and profilin1, as well as its Drosophila homolog chickadee, but not profilin2 have been implicated in the cellular defects of fragile X syndrome (FXS) pathology (Reeve et al., 2005; Michaelsen-Preusse et al., 2016).