Hypophosphatasia (HPP) is a rare heritable metabolic disorder characterized by defective mineralization of bone and/or teeth in the presence of reduced activity of unfractionated serum alkaline phosphatase (ALP). The clinical spectrum is extremely wide, from stillbirth at one end to fractures of the lower extremities in adulthood, at the other, or even no bone manifestations (odontohypophosphatasia). The disease is hypophosphatasia (MONDO_0018570). Also known as: HPP, Rathburn disease, deficiency of alkaline phosphatase, deficiency of alkaline phosphatase (disorder) [ambiguous], phosphoethanolaminuria.