ABCC6 belongs to the adenosine triphosphate-binding cassette (ABC) gene subfamily C. This protein family is involved in a large variety of physiological processes, such as signal transduction, protein secretion, drug and antibiotic resistance, and antigen presentation [Kool et al. (1999) 59:175-182; Borst and Elferink (2002) 71:537-592]. ABCC6 is primarily and highly expressed in the liver and kidney [Kool et al. (1999) 59:175-182; Bergen et al. (2000) 25:228-2231]. The precise physiological function and natural substrate(s) transported by ABCC6 are unknown, but the protein may be involved in active transport of intracellular compounds to the extracellular environment [Kool et al. (1999) 59:175-182] [Scheffer et al. (2002) 82:515-518]. Recently, it was shown that loss of function mutations in ABCC6 cause pseudoxanthoma elasticum (PXE) [Bergen et al. (2000) 25:228-2231; Le Saux et al. (2000) 25:223-227]. PXE is an autosomal recessively inherited multi-organ disorder [Goodman et al. (1963) 42:297-334; Lebwohl et al. (1994) 30:103-107]. PXE is primarily associated with the accumulation of mineralized and fragmented elastic fibers of the connective tissue in the skin [Neldner (1988) 6:1-159], BruchÂ¿s membrane in the retina [Hu et al. (2003) 48:424-438], and vessel walls [Kornet et al. (2004) 30:1041-1048]. PXE patients usually have skin lesions and breaks in BruchÂ¿s membrane of the retina (angioid streaks). Also, a variety of cardiovascular complications has been observed [Hu et al. (2003) 48:424-438]. Recently, a mouse model for PXE was created by targeted disruption of Abcc6 [Gorgels et al. (2005) 14:1763-1773; Klement et al. (2005) 25:8299-8310], which may be useful to elucidate the precise function of Abcc6 and to develop experimental therapies.