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What is hypophosphatasia (HPP)?

Hypophosphatasia (hypo-fahs-fuh-TAY-shuh), or HPP, is a progressive disease with a lifelong impact. It is a rare disease that can affect men and women of any age, from infancy through adulthood. Some people with HPP are diagnosed as children, while others are diagnosed as adults.1

Some quick facts about HPP

  • It is progressive, so symptoms may get worse over time1-3
  • New symptoms can appear at any age1
  • People with HPP can experience signs and symptoms in their bones, muscles, joints, teeth, lungs, brain, and kidneys1
  • HPP is often misdiagnosed as other more common diseases1
  • It is an inherited disease that can damage bones and bodies1

Some people who are diagnosed with HPP in adulthood report having signs and symptoms as children.4

The science behind HPP

HPP is an inherited disorder, which means the cause of HPP can be traced back to your genes.1

Genes hold the information to build and maintain the cells that make up our bodies. Specifically, genes are the instructions to make certain molecules called proteins. Some of these proteins, called enzymes , help facilitate body processes (such as building bones). One gene makes an enzyme called alkaline phosphatase ( ALP ). In people with HPP, this gene is abnormal (or mutated), resulting in low levels of the ALP enzyme.1

  • ALP plays a key role in bone mineralization and maintenance5
  • Normally, ALP allows calcium and phosphate to bind together to form healthy mineralized bones5
  • In people with HPP, ALP is low, so bone-building calcium and phosphate cannot mineralize
  • Instead, calcium and phosphate can build up in other places throughout the body, causing damage to bones and organs. In addition to calcium and phosphate, other by-products related to ALP build up where they should not. When this happens, damage to bones and other organs can occur1

A closer look at how HPP can impact your bones and body

In people who do not have HPP, the ALP enzyme helps build strong and healthy bones.

Specifically, ALP changes inorganic pyrophosphate, a molecule that normally prevents bone formation, into 2 phosphate molecules that help bone formation. These phosphate molecules bind together with calcium to mineralize bone. Bones change and rebuild themselves continually over a lifetime—which keeps both the bones and the body healthy.6

In HPP, ALP is low, so less phosphate is available to bind with calcium and form strong bones. Therefore, in people with HPP, bones can be soft or weak.7

Because bones rebuild over a lifetime, the impact of low ALP is ongoing and prevents healthy bones from being maintained. In people with HPP, calcium and inorganic pyrophosphate can build up in other parts of the body such as the kidneys, muscles, and joints. This can cause damage to organs and may lead to bone, muscle, and joint pain.1

Because HPP is an inherited disease, multiple people in the same family may have it.1 If you have HPP, your family members may want to speak with a doctor about being tested for HPP. Conversely, if someone in your family has HPP and you are having symptoms of the disease, you may want to speak with your doctor about being tested for HPP.