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Reviewed September 2007
What is hypophosphatasia?
Hypophosphatasia is an inherited disorder that affects the development of bones and teeth. This condition disrupts a process called mineralization, in which minerals such as calcium and phosphorus are deposited in developing bones and teeth. Mineralization is critical for the formation of bones that are strong and rigid and teeth that can withstand chewing and grinding.
The signs and symptoms of hypophosphatasia vary widely and can appear anywhere from before birth to adulthood. The most severe forms of the disorder tend to occur before birth and in early infancy. Hypophosphatasia weakens and softens the bones, causing skeletal abnormalities similar to another childhood bone disorder called rickets. Affected infants are born with short limbs, an abnormally shaped chest, and soft skull bones. Additional complications in infancy include poor feeding and a failure to gain weight, respiratory problems, and high levels of calcium in the blood (hypercalcemia), which can lead to recurrent vomiting and kidney problems. These complications are life-threatening in some cases.
The forms of hypophosphatasia that appear in childhood or adulthood are typically less severe than those that appear in infancy. Early loss of primary (baby) teeth is one of the first signs of the condition in children. Affected children may have short stature with bowed legs or knock knees, enlarged wrist and ankle joints, and an abnormal skull shape. Adult forms of hypophosphatasia are characterized by a softening of the bones known as osteomalacia. In adults, recurrent fractures in the foot and thigh bones can lead to chronic pain. Affected adults may lose their secondary (adult) teeth prematurely and are at increased risk for joint pain and inflammation.
The mildest form of this condition, called odontohypophosphatasia, only affects the teeth. People with this disorder typically experience abnormal tooth development and premature tooth loss, but do not have the skeletal abnormalities seen in other forms of hypophosphatasia.
How common is hypophosphatasia?
Severe forms of hypophosphatasia affect an estimated 1 in 100,000 newborns. Milder cases, such as those that appear in childhood or adulthood, probably occur more frequently.
Hypophosphatasia has been reported worldwide in people of various ethnic backgrounds. This condition appears to be most common in white populations. It is particularly frequent in a Mennonite population in Manitoba, Canada, where about 1 in 2,500 infants is born with severe features of the condition.
What genes are related to hypophosphatasia?
Mutations in the ALPL gene cause hypophosphatasia.
The ALPL gene provides instructions for making an enzyme called alkaline phosphatase. This enzyme plays an essential role in mineralization of the skeleton and teeth. Mutations in the ALPL gene lead to the production of an abnormal version of alkaline phosphatase that cannot participate effectively in the mineralization process. A shortage of alkaline phosphatase allows several other substances, which are normally processed by the enzyme, to build up abnormally in the body. Researchers believe that a buildup of one of these compounds, inorganic pyrophosphate (PPi), underlies the defective mineralization of bones and teeth in people with hypophosphatasia.
ALPL mutations that almost completely eliminate the activity of alkaline phosphatase usually result in the more severe forms of hypophosphatasia. Other mutations, which reduce but do not eliminate the activity of the enzyme, are often responsible for milder forms of the condition.
Read more about the ALPL gene.
How do people inherit hypophosphatasia?
The severe forms of hypophosphatasia that appear early in life are inherited in an autosomal recessive pattern. Autosomal recessive inheritance means that two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder each carry one copy of the altered gene but do not show signs and symptoms of the disorder.
Milder forms of hypophosphatasia can have either an autosomal recessive or an autosomal dominant pattern of inheritance. Autosomal dominant inheritance means that one copy of the altered gene in each cell is sufficient to cause the disorder.
Where can I find information about diagnosis or management of hypophosphatasia?
These resources address the diagnosis or management of hypophosphatasia and may include treatment providers.
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about hypophosphatasia?
You may find the following resources about hypophosphatasia helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for hypophosphatasia?
What if I still have specific questions about hypophosphatasia?
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding hypophosphatasia?
agenesis ; autosomal ; autosomal dominant ; autosomal recessive ; calcium ; cell ; cementum ; chronic ; deficiency ; enzyme ; gene ; hypercalcemia ; inflammation ; inheritance ; inherited ; joint ; kidney ; osteomalacia ; pattern of inheritance ; phosphatase ; phosphorus ; population ; recessive ; respiratory ; rickets ; short stature ; stature
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (5 links)
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.