COL4A4 and Alport syndrome: Alport syndrome is caused by mutations in the COL4A3 (OMIM, # 120070), COL4A4 (OMIM, # 120131), or COL4A5 (OMIM, # 303630) genes encoding collagen IVα3, α4, and α5 chains (Barker et al., 1990; Gross, 2008; Mochizuki et al., 1994).