ENPP1 and arterial calcification, generalized, of infancy, 1: Deficient generation of PPi from extracellular ATP, due to mutations in the gene encoding ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), leads to a disease known as generalized arterial calcification of infancy (GACI) (Rutsch et al., 2003).