ABCC6 and Pseudoxanthoma elasticum: As discussed above, vitamin K or one of its derivatives is not a substrate transported by ABCC6, though the depleted levels of circulating vitamin K in PXE patients was thought to have a direct consequence in the carboxylation (activation) status of the calcification inhibitor MGP and the susceptibility to chronic calcification in PXE (Gheduzzi et al., 2007; Vanakker et al., 2007, 2010).