CTNNB1 and severe intellectual disability-progressive spastic diplegia syndrome: Following the initial discoveries of gain-of-function mutations in Ctnnb1 linked to oncogenesis (Harada et al. 1999; Chalamalasetty et al. 2016; Arnold et al. 2020; Loesch et al. 2022; AmeliMojarad et al. 2023; Cai et al. 2024), numerous de novo mutations have been identified and linked to CTNNB1 syndrome, a severe neurodevelopmental disorder.