X‐linked dominant inheritance pattern (XLAS, OMIM no. 301050) due to mutations in COL4A5, which is located in the Xq22 region (Pirson, 1999), accounts for approximately 65% of patients with Alport syndrome; autosomal dominant (ADAS, OMIM no.104200) due to COL4A3 or COL4A4 heterozygous mutations located in 2q36.3 are related to approximately 20% of patients, and the remaining 15% are autosomal recessive (ARAS, OMIM no. 203780) due to biallelic mutations in COL4A3 or COL4A4 (Kashtan, 1993). The gene discussed is COL4A4; the disease is X-linked hydrocephalus with stenosis of the aqueduct of Sylvius.