A form of L1 syndrome caused by changes in the L1CAM gene characterized by severe hydrocephalus mostly with prenatal onset, signs of intracranial hypertension, adducted thumbs, spasticity, and severe intellectual deficit. HSAS represents the severe end of the spectrum and is associated with poor prognosis. The disease is MONDO_0010611 (X-linked hydrocephalus with stenosis of the aqueduct of Sylvius). Also known as: Bickers-Adams syndrome, HSAS, X-linked HSAS, X-linked acqueductal stenosis, X-linked hydrocephalus, X-linked hydrocephalus with stenosis of aqueduct of Sylvius, hydrocephalus due to aqueductal stenosis, X-linked recessive, hydrocephalus with congenital idiopathic intestinal pseudoobstruction, X-linked recessive.