Current animal models of FXS, both invertebrate (Drosophila, fruit fly [10,11,12]) and vertebrate (Mus, mouse; Rattus, rat; Danio, zebrafish [13,14,15,16,17,18,19]), have focused on loss-of-function models with disruption or knockout (KO) of the FMR1 gene homolog. The gene discussed is FMR1; the disease is fragile X syndrome.