L1CAM and congenital hydrocephalus: Pathogenic variations in AP1S2 have then been shown causal in congenital hydrocephalus, including cases with L1CAM-like phenotypic spectrum, which was therefore recognized as a separate X-linked syndrome, named Fried-Pettigrew syndrome (OMIM #304,340), characterized primarily by intellectual disability, basal ganglia iron or calcium deposition and hydrocephalus also associated to aqueductal stenosis.