ABCC6 and Pseudoxanthoma elasticum: We have previously shown that the higher RPE maturation level increases the response amplitudes [14]; thus, further studies are needed to conclude if the PXE-specific RPE cells were more immature (although highly pigmented) with the phenotype or if the ABCC6 mutation has some still unknown function in the barrier properties, phagocytosis or ATP signaling responses of RPE.