Fibulin 3: A protein that belongs to a family of extracellular proteins expressed in the basement membranes of blood vessels. The gene that encodes fibulin 3 is FBLN3 (or EFEMP1). FBLN3 is located on chromosome 2 in band 2p16. A single mutation in FBLN3 is responsible for an autosomal dominant form of macular degeneration. See also: Fibulin 5.