In Fmr1 KO mice that have been engineered to remove one App allele, there is a significant reduction in expression of Aβ and multiple phenotypes of FXS, including the presence of audiogenic seizures, the ratio of immature dendritic spines to mature spines, and long-term depression, were partially or fully corrected after removal of the App allele [66]. This evidence concerns the gene FMR1 and fragile X syndrome.