ENPP1 and Pseudoxanthoma elasticum: It has been recently demonstrated that other genes such as ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1) and GGCX (γ-glutamyl carboxylase), in addition to ABCC6, have a pathogenic role in calcification-associated diseases (e.g., PXE), as suggested by the occurrence of digenic inheritance [3,4,5].