ENPP1 and arterial calcification, generalized, of infancy, 1: This is well evidenced by the fact that homozygous ENPP1 deficiency in humans leads to a severe form of vascular calcification (GACI; Generalized Arterial Calcification of Infancy) and that loss of function mutations in ENPP1 leads to spine stiffening (OPLL, Ossification of the Posterior Longitudinal Ligament), both of which are recapitulated in mouse models (20–23).