COL4A5 and X-linked Alport syndrome: Thus, two of the commonest hypomorphic variants are p.Gly624Asp in COL4A5 and p.Leu1474Pro in COL4A3. p.Gly624Asp in COL4A5 is found in about one in 3,000 of the European population or about one quarter of all Europeans with X-linked Alport syndrome (20, 41).