The American Society for Bone and Mineral Research (ASBMR) held its Annual Meeting from October 13 to 16, 2023. During the meeting, over 2,000 attendees and stakeholders came together to share insights and explore up-and-coming bone, mineral and musculoskeletal research. According to a news release from Kyowa Kirin, Inc., the company presented data from two studies which sought to (1) explore the long-term burden of X-linked hypophosphatemia (XLH), and (2) identify the clinical characteristics of XLH that physicians can use to better understand this condition.

The ASBMR Studies

Study #1: Exploring XLH and Disease History in People Using Burosumab

In this study, researchers sourced data from 1,358 individuals with X-linked hypophosphatemia. They identified patients using the Healthcare Map from Komodo Health and specifically focused on people who were treated using burosumab (marketed under the brand name Crysvita). Crysvita is a human monoclonal antibody directed against FGF23; it is administered via injection. Learn more about Crysvita here.

After evaluating the data, the researchers found that people with XLH often faced significant and severe complications, many of which increased or worsened with age. These complications included, but were not limited to joint and muscle pain, a type of degenerative joint disease called osteoarthritis, depression, high blood pressure, bone fracturing, and obesity. The findings also found that most people had already tried taking therapies like calcitriol prior to beginning burosumab.

Study #2: Clinical Characteristics of People with Familial Hypophosphatemia

This retrospective study utilized data from healthcare claims in 570 people with familial hypophosphatemia and 1,710 people who did not have this condition. While not every case of familial hypophosphatemia is XLH, about 80% of them are considered XLH. If patients had ever used burosumab for treatment, their information was not used in this study. Researchers confirmed that people with familial hypophosphatemia had higher rates of kidney disease, joint and muscle pain, bone fracturing, and osteoarthritis. Depression, obesity, and high blood pressure were also significantly more common.

CRYSVITA Information

Crysvita is safe and relatively well-tolerated. It plays a role in phosphorus reabsorption and vitamin D production, both of which are abnormal in XLH. While this treatment is safe, some side effects have been observed. These include injection-site reactions, fever, muscle and extremity pain, rash, diarrhea or constipation, nausea and vomiting, cough, or dental issues such as tooth abscesses.

What You Need to Know: X-Linked Hypophosphatemia (XLH)

X-linked hypophosphatemia results from PHEX mutations on the X chromosome. It is inherited in 70-80% of cases and occurs spontaneously in the other 20-30%. These mutations cause increases in a growth hormone called FGF23 that regulates phosphate reabsorption in the kidneys. As a result, phosphorus blood levels are low and phosphorus is excreted through urine, leading to bone abnormalities and defects. This rare inherited disorder affects an estimated 1 in every 20,000 people. Typically, symptoms appear in early childhood and may include:

• Weak or fragile bones
• Bone, joint, or tooth pain
• Early osteoarthritis
• Enlarged or swollen wrists/ankles
• Abnormal or waddling gait
• Easily dislocated joints
• Hearing loss
• Spinal stenosis
• Hip bone abnormalities
• Short stature
• Bowed or bent legs

Do you or a loved one have XLH and you’re looking for support? Check out the XLH Network for resources.