Rare Disease Spotlight: X-Linked Hypophosphatemia

By Barby Ingle, PNN Columnist  

Coming off a successful Rare Disease Awareness worldwide campaign in February, I decided to go with X-Linked Hypophosphatemia (XLH) for my rare disease spotlight this month.

I do know a little about this disease, having a friend from childhood that lived with a form of it. Back then, it was known as rickets, a softening and weakening of the bones in children. I also served on a patient advisory board a few years ago for a company that created the only FDA-approved treatment for XLH.

Rickets is caused by Vitamin D deficiency, while XLH is caused by a genetic mutation that causes the body to lose phosphorous, an important ingredient for bone health. XLH cannot be cured, but its progression can be slowed with phosphate, Vitamin D and calcium supplementation.

Like rickets, XLH can cause bone deformities. Being bow-legged is the most recognizable symptom, giving providers a visible clue as to which rare disease to test for when they are uncertain. About 1 in 20,000 people carry the genetic mutation that causes XLH.   

The symptoms for XLH vary for each patient, just as they do for other conditions. The most common ones include osteoarthritis, poor bone health, bone pain, low bone density, bones that easily fracture, short stature, bow-leggedness, major tooth abscesses, large dental pulp, tinnitus, waddling gait, muscle pain and body weakness.

As I mentioned, there is only one approved medication for this disease. The drug Crysvita (burosumab) helps normalize phosphate levels and is indicated for the treatment of XLH in adults and children 6 months of age and older.

The severe bow-leggedness caused by XLH can be treated with surgery to correct and reshape the legs. For less severe cases, phosphate supplements and growth hormones can help strengthen bones. Corrective dental treatments can also help with tooth abscesses and dental pulp issues.

If you’d like to learn more about XLH, there are a few sites that I have found helpful. These include the XLH Network, a nonprofit support group, and the National Institutes of Health’s Rare Diseases Information Center. You can also get information about XLH by visiting the website for Ultragenyx, the company that makes Crysvita.

I really like this video of a family affected by XLH. The children do a great job sharing their story.

When I was growing up, we did not have as much knowledge or awareness about rare diseases as we do now. We expected people with rare conditions back then to get by with little to no assistance. Today we know more and have more treatments, but we still have a long way to go.

I know what it meant to my young friend to get support when we knew far less about XLH. She was able to live a full life, attend school, and participated in gymnastics and cheerleading with me. But she suffered more injuries than most kids, was made fun of for her bow legs, and endured daily physical pain.

I dedicate this rare disease spotlight to my friend.

Barby Ingle lives with reflex sympathetic dystrophy (RSD), migralepsy and endometriosis. Barby is a chronic pain educator, patient advocate, and president of the International Pain Foundation. She is also a motivational speaker and best-selling author on pain topics. More information about Barby can be found at her website.