CTNNB1 syndrome is a neurodevelopmental disorder characterized by intellectual disability, global developmental delay, microcephaly and motor disabilities, among others, caused by pathogenic loss-of-function variants in the CTNNB1 gene, which encodes β-catenin. This syndrome has no treatment option, with only supportive care available. To address this unmet medical need, researchers from the Broad Institute and Tufts University School of Biomedical Sciences have developed a Ctnnb1 germline heterozygote murine model that mimics the human CTNNB1 syndrome.