Congenital hypophosphatasia is absence or low levels of serum alkaline phosphatase due to mutations in the gene encoding tissue nonspecific alkaline phosphatase.

Because serum alkaline phosphatase is absent or decreased, Ca⁺⁺ is not diffusely deposited in bones, causing low bone density and hypercalcemia. Alkaline phosphatase deficiency also causes intracellular pyridoxine (vitamin B₆) deficiency, which can cause generalized seizures. Vomiting, inability to gain weight, and enlargement of the epiphyses (similar to that in rickets) usually occur. Patients who survive infancy have bony deformities and short stature, but mental development is normal.

No treatment is effective, but infusions of alkaline phosphatase and bone marrow transplantation have limited roles. Vitamin B₆ in high doses may reduce seizures; 50 to 100 mg IV is given once for an active seizure, followed by 50 to 100 mg po once/day). NSAIDs reduce bone pain.

Last full review/revision May 2013 by David D. Sherry, MD; Frank Pessler, MD, PhD

Content last modified May 2013