COL4A4 and X-linked hydrocephalus with stenosis of the aqueduct of Sylvius: Pathogenic variants in COL4A5 usually cause X-linked Alport syndrome (XLAS), while alterations in COL4A3 and COL4A4 genes are associated with autosomal dominant AS (ADAS) or autosomal recessive AS (ARAS) (4–6).