Hypophosphatasia.

Hypophosphatasia (HPP) is a rare, inherited, potentially life-threatening metabolic disorder that arises from loss-of-function mutations in the gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). As a result of these mutations (as many as 260 genetic mutations have been associated with HPP), patients have disordered bone mineralization leading to rickets, osteomalacia, fractures and other skeletal abnormalities as well as other systemic complications such as seizures, respiratory compromise, dental anomalies, nephrocalcinosis and/or weakness and chronic pain. HPP may appear across the age spectrum, from in utero, to infancy, childhood, adolescence and/or adulthood. More severe cases tend to be seen in utero and infancy, and in these instances, mortality may be as high as 50%. In surviving or older patients, disability and poor quality of life may be seen. Based on clinical presentation, HPP can be mistakenly diagnosed as other skeletal diseases, but a low alkaline phosphatase is an important, distinguishing sign of this condition. While patients with HPP may benefit from supportive measures, at the present time, there is no approved specific therapy for HPP.