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Case study: A new drug for a rare disease

Lottie and her younger brother Ashley have a rare disease called X-linked hypophosphataemic rickets. They took part in a clinical trial of a new drug called burosumab at the NIHR Great Ormond Street Hospital Clinical Research Facility. Following the trial, burosumab is now available to patients on the NHS.

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The Challenge

A disease or disorder is defined as rare in Europe when it affects fewer than 1 in 2000 people. It is estimated that 1 in 17 people will experience a rare disease at some point in their life.

X-linked hypophosphataemic rickets (XLH) is a rare form of rickets that affects around 300 children in the UK.

XLH is caused by genetic mutation that makes the body produce too much of a protein called fibroblast growth factor (FGF23). This means the kidneys leak phosphate into the urine, causing joint pains, weaker bones, bowing of the legs and impaired growth.

The current treatment for XLH is taking phosphate salts and vitamin D several times a day. This increases the level of phosphate in the blood, but doesn’t significantly improve bone-related symptoms and is associated with side effects.

Our research

The NIHR Clinical Research Facilities at Great Ormond Street HospitalManchester and Birmingham were part of an international research study to assess a new, targeted drug for children with XLH. The drug, called burosumab, inhibits the activity of FGF23 and reduces phosphate loss in the urine.

Children aged 5-12 years old were treated every two or four weeks with burosomab at the three NIHR Clinical Research Facilities, as well as at research facilities in the USA, the Netherlands and France.

The research, published in the New England Journal of Medicine, found that children reported less pain after 64 weeks of treatment. Joint X-rays showed a 50% reduction in disease severity and significantly improved growth rates.

The National Institute for Health and Care Excellence has approved burosumab to treat X-linked hypophosphataemia in children and young people. The drug became available on the NHS from January 2019, only four years after the phase 2 trial first started.

This research is just one example of how precision medicine is helping to develop targeted treatments for children with rare and complex health conditions. Burosumab is first drug to act directly on the cause of XLH and holds promise for improving long-term outcomes for affected children, representing an important advance for them and their families.

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Patient story

Lottie 14, and her younger brother Ashley, 12, both have XLH. Lottie and Ashley took part in the clinical trial of burosumab at the NIHR GOSH Clinical Research Facility.

At the facility they received regular injections of the new drug to maintain the level of phosphate in their blood. “To start with the injections were quite hard - but eventually I got used to them and then it was fine,” said Ashley.

“I didn't expect the nurses and doctors to be so nice. I thought they would just do the medicines and go,” Lottie said. “They all spend lots of time with my brother and I and they are all kind!”

Both Lottie and Ashley are keen to help others with their condition. Lottie said: “I joined the trial to help me and my family with my genetic condition.” Ashley added: “My parents told me it could help other people with our condition and it would help my family too, lots of us have XLH.”

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