CTNNB1 Neurodevelopmental Syndrome

The goal of this first in human, phase I/II clinical trial is to evaulate the safety, tolerability, and preliminary efficacy of AAV9 mediated gene replacement therapy (Urbagen) in paediatric patients with CTNNB1 neurodevelopmental disorder. The main questions it aims to answer are: * Is the gene therapy with Urbagen safe and well tolerated? * Does the gene therapy improve motor function, cognitive function, behavior, sleep, and/or quality of life? Participants will: * Undergo screening assessments to ensure eligibility. * Recieve a single dose of gene therapy via bilateral intracerebroventricular administration. * Recieve prophylactic immunosuppresants (methylprednisolone, sirolimus). * Attend follow-up visits for safety monitoring and clinical assessments over the course of three years.

The aim of the Dragonfly study is to characterise and monitor the neurodevelopment of children and adults diagnosed with CTNNB1 syndrome through an international collaborative effort. Gaining comprehensive understanding of the mental, physical and social development of people with CTNNB1 neurodevelopmental syndrome and how their symptoms and abilities change over time will help improve and standardize care for these patients, as well as facilitate future research and clinical trials design.