"Hypophosphatasia is an inherited metabolic (chemical) bone disease that results from low levels of an enzyme called alkaline phosphatase (ALP).

Enzymes are proteins that act in the body's chemical reactions by breaking down other chemicals. ALP is normally present in large amounts in bone and liver.

In hypophosphatasia, abnormalities in the gene that makes ALP lead to production of inactive ALP. Subsequently, several chemicals -- including phosphoethanolamine, pyridoxal 5'-phosphate (a form of vitamin B6) and inorganic pyrophosphate -- accumulate in the body and are found in large amounts in the blood and urine.

It appears that the accumulation of inorganic pyrophosphate is the cause of the characteristic defective calcification of bones in infants and children (rickets) and in adults (osteomalacia)."

There are six clinical forms of hypophosphatasia -- perinatal, infantile, childhood, odontohypophosphatasia, pseudohypophosphatasia and the adult form.