Fibulin 5: A protein that belongs to a family of extracellular proteins expressed in the basement membranes of blood vessels. Fibulin 5 may be essential for the polymerization of elastin. Missense mutations in FBLN5, the gene that encodes fibulin 5, appear responsible for 1-2% of cases of age-related macular degeneration (AMD). FBLN5 is located on chromosome 14 in band 14q32.1. See also: Fibulin 3.