summary Hypophosphatasia is a metabolic bone disease caused by a mutation in the isoenzyme of alkaline phosphatase that leads to low levels of alkaline phosphate and generalized impairment of bone mineralization. Patients present with clinical manifestations similar to rickets with bow legs, short stature, abnormal teeth, and increased susceptibility to fractures. Diagnosis is made with the presence of phosphoethanolamine in the urine. Treatment modalities are currently under investigation. Epidemiology Incidence estimated to be 1 in 100,000 Etiology Pathophysiology low levels of alkaline phosphate result in decreased synthesis of inorganic phosphate necessary for bone matrix formation osteoid that forms in the hypertrophic zone of the growth plate fails to mineralize the zone of provisional calcification never forms and growth is inhibited Genetics inheritance pattern autosomal recessive caused by a mutation in the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP) Associated conditions orthopaedic manifestations similar to rickets bow legs short stature non-orthopaedic manifestations abnormal tooth formation loss of teeth Presentation Clinical findings presentation similar to rickets genu varum short stature abnormal dentition Imaging Radiographs recommended AP and lateral of affected bone findings abnormal bone formation "deossification of bone" adjacent to growth plate physeal widening Evaluation Labs serum decreased serum alkaline phosphatase urine phosphoethanolamine in the urine diagnostic for hypophosphatasia Treatment Nonoperative no approved therapies phosphate therapy under investigation but not utilized at this time