X-linked AS (XLAS), the most common form, accounts for about 85% of AS patients, which is ascribed to variants in the collagen type IV alpha 5 chain gene (COL4A5) (Slajpah et al., 2007; Nabais Sá et al., 2015). Here, COL4A5 is linked to X-linked hydrocephalus with stenosis of the aqueduct of Sylvius.