L1CAM and congenital hydrocephalus: In particular, stenosis of the Aqueduct of Sylvius, that connects the third and fourth ventricles, accounts for the majority of cases of non-syndromic (no extra-cerebral feature) congenital hydrocephalus, of whom 5–15% have an X-linked form due to variations in L1CAM that are associated to a wide phenotypic spectrum [2].