Loss-of-function mutations in the CTNNB1 gene cause β-catenin deficiency, leading to CTNNB1 syndrome, a rare neurodevelopmental disorder marked by motor and cognitive impairments. Because the disease stems from single-allele mutations that vary widely, a broadly applicable corrective strategy is needed. Since CTNNB1 is dosage-sensitive, therapies must preserve normal regulation, and in some cases may also need to suppress harmful mutant transcripts.