COL4A5 and X-linked hydrocephalus with stenosis of the aqueduct of Sylvius: In family 3, in which we detected a COL4A5 donor splice site mutation (c.687 + 1G > A) known to cause XLAS, the disease was unusually severe (for X-linked disease) in the female patients I-2, II-2 and II-5 and unusually mild in the male patient III-2.