The molecular etiology is covered by reviews on the transcriptional regulation of the ABCC6 gene and the role of modifier genes in PXE, while a contribution on ENPP1 and the overlapping phenotype between PXE and Generalized Arterial Calcification of Infancy (GACI) makes the transition to clinical papers on specific aspects of the PXE retinopathy and vasculopathy. The gene discussed is ABCC6; the disease is Pseudoxanthoma elasticum.