The emerging importance of ABC A-transporters in human disease is reflected by the fact that as yet four members of this protein family (ABCA1, ABCA3, ABCR/ABCA4, ABCA12) have been causatively linked to completely unrelated groups of monogenetic disorders including familial high-density lipoprotein (HDL) deficiency, neonatal surfactant deficiency, degenerative retinopathies and congenital keratinization disorders.