Hypophosphatasia (HPP)
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Program
What Is Hypophosphatasia?
Hypophosphatasia (HPP) is a rare genetic condition that affects bones. In people with HPP, bones and teeth do not absorb enough calcium and phosphorus, which makes them soft and weak. These soft bones are at risk of breaking more easily (fractures).
What Causes Hypophosphatasia?
HPP is caused by changes (variants) in a gene called ALPL. This gene controls how much of an enzyme called alkaline phosphatase (ALP) the body makes. ALP helps bones absorb calcium and phosphorus from the blood. Without enough ALP, bones cannot use these important nutrients and become weak.
What Are the Signs & Symptoms of Hypophosphatasia?
There are different types of HPP, and symptoms can vary. Some children have severe symptoms shortly after birth, while others have mild symptoms later in childhood, adolescence or adulthood.
Common signs and symptoms include:
- Early loss of baby teeth (with the whole root of the tooth still attached)
- Short height
- Skeletal deformities, such as:
- Bowed legs
- Enlarged wrists and ankles
- Abnormal head shape
- Bone or joint pain
- Frequent fractures (broken bones)
- Gait abnormalities/trouble walking
In babies, additional symptoms may include:
- Difficulty feeding
- Poor weight gain
- Breathing problems
- High calcium levels
- Seizures that get better with Vitamin B6
How Is Hypophosphatasia Diagnosed?
Your provider may check for HPP using blood tests to measure ALP levels and other markers like calcium, phosphorus, and Vitamin B6. Genetic testing can look for changes in the ALPL gene. Imaging tests like X-rays or bone density scans (DXA) can also help confirm the diagnosis.
How Is Hypophosphatasia Treated?
Treatment depends on how severe the symptoms are:
- Mild cases: Physical therapy and over-the-counter pain medicine like acetaminophen, ibuprofen, or naproxen are often the recommended treatments.
- Severe cases: A medication called asfotase alfa is used. This is an enzyme replacement therapy that helps the body get the ALP it needs. It is given as an injection 3 to 6 times a week.
What Are the Long-Term Effects of Hypophosphatasia?
The long-term effects of HPP depend on the type of HPP. Severe forms that appear in infancy can be life-threatening if not treated early. All types of HPP increase the risk of fractures.
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