Know your IMD: Hypophosphatasia

Know your IMD: Hypophosphatasia (HPP)

What is it?

Hypophosphatasia (HPP) is an inherited disorder that affects the development of bones and teeth. This condition disrupts a process called mineralisation, 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.

Symptoms

Hypophosphatasia weakens and softens the bones, causing skeletal abnormalities Affected infants are born with short limbs, an abnormally shaped chest, and soft skull bones. Perinatal HPP blocks skeletal mineralisation, including in the womb which lead to deformities, with some pregnancies ending in stillbirth, whilst some affected newborns survive for several days, but if untreated die from respiratory failure due to deformities and weakness of the chest.

Additional complications in infancy include poor feeding and a failure to gain weight, respiratory problems, and high levels of calcium in the blood, which can lead to recurrent vomiting and kidney problems. These complications are lifethreatening in some cases.

The forms of hypophosphatasia that appear in childhood or adulthood are typically less severe than those that appear in infancy. Affected children may have short stature with bowed legs or knock knees, enlarged wrist and ankle joints, and an abnormal skull shape. Some children lose "baby " teeth in infancy or early childhood, this is known as odontohypophosphatasia.

Adult forms of hypophosphatasia are characterised by fatigue, reduced mobility and a softening of the bones known as osteomalacia. Some adults experience recurrent fractures in the foot and thigh bones which can lead to chronic pain. Affected adults may lose their secondary (adult) teeth prematurely and are at increased risk for joint pain and inflammation.

How is it treated?

Strensiq is used to treat perinatal, infantile, and juvenile onset HPP and managed access agreements have provided limited cover to UK adults.

Treatment is symptomatic and supportive. Some patients who have paediatriconset forms may also be able to access Strensiq on the managed access agreement as part of NICE appraisal (For more on the managed access agreement for Strensiq, visit the following link: https://bit.ly/3MVPmq8)

Other treatments target specific symptoms and complications.

-Non-steroidal anti-inflammatory drugs to treat bone and joint pain -Vitamin B6 to help to control seizures in severely affected infants -Regular dental care beginning early on -Physical and occupational therapy -Surgery -Metal rod insertion to strengthen bones -Orthotic braces

Metabolic Support UK strongly supports our HPP community, continually advocating for continued access to Strensiq, and supporting individuals throughout every other aspect to ensure that despite diagnosis, they have the best quality of life possible.

To learn more about HPP, email jonathan@metabolicsupportuk.org for a copy of our HPP insight presentation.