ENPP1 and Pseudoxanthoma elasticum: Pseudoxanthoma elasticum (PXE; OMIM# 264800) is an autosomal recessive metabolic disease caused by loss-of-function pathogenic variants in the ABCC6 (ATP-binding cassette, subfamily C, member 6) gene and—to a much lesser extent—the ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1) gene [47,48].