FMR1 and fragile X syndrome: In this work, genetic reduction of APP expression in Fmr1 KO mice has been demonstrated to rescue neuronal hyperexcitability (Westmark et al., 2011b, 2016a), a well-documented neural phenotype in Fmr1 KO mice, FXS humans, and slice physiology (Gibson et al., 2008; Choi et al., 2015; Ethridge et al., 2016, 2017; Westmark et al., 2016a; Lovelace et al., 2018).