CRB2 and obstructive hydrocephalus: Hydrocephalus associated to bi-allelic variations in CRB2, MPDZ and CCDC88C constitutes a separate pathogenic group of congenital non-communicating hydrocephalus with Sylvius aqueduct and central canal of the medulla atresia that might be linked to disturbed apical constriction of the ventricular layer cells, a complex remodeling process required for the formation of the central canal of the medulla.