Hypophosphatasia
Hypophosphatasia is one of several disorders that resembles osteogenesis imperfecta. It is an inherited metabolic (chemical) bone disease that results from low levels of an enzyme called alkaline phosphatase (ALP). Enzymes are proteins that break down other chemicals in the body so the body can use them. ALP is normally present in large amounts in bones and the liver. In hypophosphatasia, abnormalities in the gene that makes ALP lead to the 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 seen in infants and children (rickets)and in adults (osteomalacia).

The severity of hypophosphatasia is remarkably variable from patient to patient. The most severely affected fail to form a skeleton in the womb and are stillborn. The mildly affected patients may show only low levels of ALP in the blood, yet never suffer bone problems.

In general, patients are categorized as having "perinatal," "infantile," "childhood," or "adult"hypophosphatasia depending on the severity of the disease and the age at which the bony manifestations are first detected. The x-ray changes are quite distinct to the trained eye, and the diagnosis is substantiated by measuring ALP in a routine blood test. It is important that the doctors use appropriate age ranges for normal ALP levels when interpreting the blood test.

Odontohypophosphatasia is a disease in which children and adults have only dental, not skeletal, problems. This usually involves premature loss of teeth.

Symptoms
There are reports of blue sclera (whites of the eyes) during infancy and childhood that may resemble osteogenesis imperfecta. Depending on the severity of the skeletal disease, there maybe deformity of the arms, legs and chest. Frequent bouts of pneumonia can result if the chest distortion is severe. Recurrent fractures can also occur. Teeth may be lost prematurely and the teeth may have wide pulp chambers that predisposes them to cavities. These symptoms resemble some of those found in osteogenesis imperfecta.
Content Courtesy : www.osteo.org
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