COL4A1 and Dilatation of the cerebral artery: AS is induced by mutations in any of three type IV collagen genes: COL4A3, COL4A4, or COL4A5. Some papers have been published on the relationship between collagen IV gene mutation and renal cysts: COL4A1 was identified as a candidate gene in hereditary angiopathy with nephropathy, aneurysms, and muscle cramps (HANAC) syndrome with AD hematuria, cystic kidney disease, intracranial aneurysms, and muscle cramps [15].