COL4A5 and X-linked hydrocephalus with stenosis of the aqueduct of Sylvius: COL4A5 (MIM #303630) is a monogenic causative gene of X‐linked Alport syndrome (XLAS; MIM #301050), which may cause end‐stage renal disease accompanied by sensorineural hearing loss and ocular abnormalities (Barker et al., 1990; Kashtan, 1998).