CTNNB1 and Down syndrome: Patients with a confirmed molecular diagnosis of CTNNB1 syndrome were prospectively recruited at the Rare Disease Unit of the Paediatrics Department, Fondazione Policlinico Agostino Gemelli IRCCS/Medical Genetics Unit, Rome, and Medical Genetics Unit, IRCCS Bambino Gesù Children Hospital, Rome from January 2021 over a period of 24 months.