ENPP1 and arterial calcification, generalized, of infancy, 1: Most GACI cases are due to biallelic variants in the gene encoding ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1) leading to ENPP1 enzyme deficiency, and less commonly due to variants in ATP-binding cassette sub-family C member 6 (ABCC6) [4].