BDNF and fragile X syndrome: Several studies indicate that brain-derived neurotrophic factor (BDNF) and its tropomyosin-related kinase B (TrkB) receptors are involved in the plasticity changes in FXS (Uutela et al., 2012; Castrén and Castrén, 2014) as well as in autism (Perry et al., 2001; Miyazaki et al., 2004; Connolly et al., 2006; Correia et al., 2011; Garcia et al., 2012).