XLAS is caused by COL4A5 gene mutations and accounts for 80% of patients with AS, while ARAS and ADAS are caused by homozygous or heterozygous mutations in COL4A3 or COL4A4 genes and account for 15% and 5% of patients with AS, respectively (Rheault & Kashtan, 2016). This evidence concerns the gene COL4A5 and X-linked hydrocephalus with stenosis of the aqueduct of Sylvius.