ABCC6 and pseudoxanthoma elasticum (inherited or acquired): The gene defect in PXE has been characterized as a loss of function mutation in the adenosine triphosphate-binding cassette subtype C number 6 gene (ABCC6).1 Modification in the extracellular matrix, which is important in the health and vitality of the retinal pigment epithelium (RPE), appears to be related this mutation.