ENPP1 and hypophosphatasia: Since PPi is produced by the enzymatic action of ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) from adenosine triphosphate (ATP), we tested if ENPP1 could be a druggable target for the development of an alternative treatment for HPP, particularly for the non-lethal later-onset forms of HPP, where enzyme replacement is not currently approved.