ENPP1 and arterial calcification, generalized, of infancy, 1: Characteristic cases of GACI, designated as GACI-1, with early onset ectopic mineralization, harbor biallelic loss-of-function mutations in the ENPP1 gene, and their circulating PPi levels, as deduced from the corresponding Enpp1−/− mouse models [19], are essentially zero, allowing early aberrant mineralization to take place with serious phenotypic consequences [20,21].