ENPP1 and arterial calcification, generalized, of infancy, 1: GACI is caused in most cases by loss-of-function mutations in the ENPP1 gene, which codes for ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), an extracellular membrane bound glycoprotein that hydrolyzes adenosine triphosphate into adenosine monophosphate and inorganic pyrophosphate (PPi) [9, 10].