Although disease-causing variants in COL4A5 lead to XLAS,10,11 variants in COL4A3 and COL4A4 result in the autosomal form, both in a biallelic (ARAS)12,13 and monoallelic (ADAS) fashion.14 This evidence concerns the gene COL4A5 and X-linked hydrocephalus with stenosis of the aqueduct of Sylvius.