In the present study we review mouse models with alterations in the Ctnnb1 gene, including gain- (GoF) and loss-of-function (LoF) models, focusing on mouse models exhibiting symptoms of neurodevelopmental disorders, including models with aberrant brain/embryo development, and motor disorders, both hallmarks of the CTNNB1 syndrome. The gene discussed is CTNNB1; the disease is Down syndrome.