• Publication in the Journal of Bone and Mineral Research offers new insight into the long-term XLH treatment experience

PRINCETON, N.J., Oct. 14, 2026 (GLOBE NEWSWIRE) -- Kyowa Kirin, Inc., a wholly owned subsidiary of Kyowa Kirin Co., Ltd. (TSE:4151, Kyowa Kirin), today announced the publication of three-year real-world findings from an interim analysis of the XLH Disease Monitoring Program (DMP) in the Journal of Bone and Mineral Research. The analysis assessed serum phosphate levels and patient-reported pain, stiffness, and physical function at years 1 and 3 among adults with X-linked hypophosphatemia (XLH) treated with burosumab or oral phosphate and active vitamin D (Pi/D). Read the full study here.

“Real-world evidence in rare diseases like XLH is invaluable, helping to deepen our understanding of the patient experience and treatment outcomes beyond clinical trials,” said lead author Steven W. Ing, MD, MSCE, Professor of Clinical Medicine, Division of Endocrinology, Diabetes and Metabolism, The Ohio State University Wexner Medical Center. “These findings add to the broader evidence base for burosumab and can help inform clinical decision-making and the ongoing evolution of care for adults living with XLH.”

XLH is a rare, lifelong, progressive genetic disease that causes excessive phosphorus loss, weakening the bones and muscles in children and adults, leading to skeletal deformities.1 The XLH DMP is a prospective, 10-year, observational study of adults and children with XLH in the US, Canada, and Latin America. It is designed to characterize XLH disease presentation and progression, and to prospectively assess changes over time in biochemical, clinical, and patient/caregiver-reported outcomes in a representative population.

No randomized studies have directly compared treatment with burosumab, a monoclonal antibody targeting FGF23, with oral phosphate and active vitamin D in adults with XLH. This three-year analysis included 109 adults enrolled in the XLH DMP: 54 who received burosumab and 55 who received Pi/D.

“For people living with a rare, lifelong condition such as XLH, it is essential to understand how treatments perform over time,” said Angela Williams, PhD, Vice President, Global Head of Health Economics and Outcomes Research at Kyowa Kirin. “By following patients longitudinally and incorporating patient-reported measures, the XLH Disease Monitoring Program provides additional context for the clinical data supporting burosumab use in adults with XLH.”

In addition to the XLH Disease Monitoring Program, Kyowa Kirin is advancing real-world insight generation through the International XLH Registry in Europe and the SUNFLOWER study in Japan and Korea.

About CRYSVITA® (burosumab-twza) Injection

CRYSVITA is a recombinant fully human monoclonal IgG1 antibody, discovered by Kyowa Kirin, which binds to and inhibits the biological activity of FGF23, the underlying cause of hypophosphatemia in XLH. By blocking FGF23, CRYSVITA helps to restore phosphorus reabsorption in the kidneys and increase the production of active vitamin D, which enhances intestinal absorption of phosphate and calcium.

U.S. CRYSVITA Indication

CRYSVITA is a fibroblast growth factor (FGF23) blocking antibody indicated for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients 6 months of age and older.

Important Safety Information

CONTRAINDICATIONS

CRYSVITA is contraindicated:

In concomitant use with oral phosphate and/or active vitamin D analogs (e.g., calcitriol, paricalcitol, doxercalciferol, calcifediol) due to the risk of hyperphosphatemia.

When serum phosphorus is within or above the normal range for age.

In patients with severe renal impairment or end stage renal disease because these conditions are associated with abnormal mineral metabolism.

WARNINGS AND PRECAUTIONS

Hypersensitivity

Hypersensitivity reactions (e.g., rash, urticaria) have been reported in patients with CRYSVITA. Discontinue CRYSVITA if serious hypersensitivity reactions occur and initiate appropriate medical treatment.

Hyperphosphatemia and Risk of Nephrocalcinosis

Increases in serum phosphorus to above the upper limit of normal may be associated with an increased risk of nephrocalcinosis. For patients already taking CRYSVITA, dose interruption and/or dose reduction may be required based on a patient's serum phosphorus levels.

Hypercalcemia

Increases in serum calcium have been reported in patients treated with CRYSVITA. Patients with risk factors such as pre-existing hyperparathyroidism, prolonged immobilization, dehydration, hypervitaminosis D, or renal impairment, are at higher risk of hypercalcemia. Monitor these patients for serum calcium and parathyroid hormone levels before and during CRYSVITA treatment for moderate to severe hypercalcemia. In patients with moderate to severe hypercalcemia, CRYSVITA should not be administered until hypercalcemia is adequately managed.

Injection Site Reactions

Administration of CRYSVITA may result in local injection site reactions. Discontinue CRYSVITA if severe injection site reactions occur and administer appropriate medical treatment.

ADVERSE REACTIONS

Pediatric Patients

Adverse reactions reported in 10% or more of CRYSVITA-treated pediatric XLH patients across three studies are: pyrexia (55%, 44%, and 62%), injection site reaction (52%, 67%, and 23%), cough (52%), vomiting (41%, 48%, and 46%), pain in extremity (38%, 46%, and 23%), headache (34% and 73%), tooth abscess (34%, 15%, and 23%), dental caries (31%), diarrhea (24%), vitamin D decreased (24%, 37%, and 15%), toothache (23% and 15%), constipation (17%), myalgia (17%), rash (14% and 27%), dizziness (15%), and nausea (10%).

Adult Patients

Adverse reactions reported in more than 5% of CRYSVITA-treated adult XLH patients and in at least 2 patients more than placebo in one study are: back pain (15%), headache (13%), tooth infection (13%), restless legs syndrome (12%), vitamin D decreased (12%), dizziness (10%), constipation (9%), muscle spasms (7%), and blood phosphorus increased (6%).

Spinal stenosis is prevalent in adults with XLH, and spinal cord compression has been reported. It is unknown if CRYSVITA therapy exacerbates spinal stenosis or spinal cord compression.

USE IN SPECIFIC POPULATIONS

There are no available data on CRYSVITA use in pregnant women to inform a drug-associated risk of adverse developmental outcomes. Serum phosphorus levels should be monitored throughout pregnancy. Report pregnancies to the Kyowa Kirin, Inc. Adverse Event reporting line at 1-844-768-3544.

There is no information regarding the presence of CRYSVITA in human milk or the effects of CRYSVITA on milk production or the breastfed infant. Therefore, the developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for CRYSVITA and any potential adverse effects on the breastfed infant from CRYSVITA or from the underlying maternal condition.

PATIENT COUNSELING INFORMATION

Advise patients not to use any oral phosphate and/or active vitamin D analog products.

Instruct patients to contact their physician if hypersensitivity reactions, injection site reactions, and restless legs syndrome induction or worsening of symptoms occur.

You may report side effects to the FDA at (800) FDA-1088 or www.fda.gov/medwatch. You may also report side effects to Kyowa Kirin, Inc. at 1-844-768-3544.

For important risk and use information, please see the full Prescribing Information for CRYSVITA.

About X-linked hypophosphatemia (XLH)

X-linked hypophosphatemia is a rare, lifelong, genetic disease that can impact the bones and muscles in both children and adults. In individuals with XLH, the body doesn't hold on to enough phosphorus, which is an essential mineral for bone health. This is due to the production of excess fibroblast growth factor 23 (FGF23), causing the body to release too much phosphorus through the urine. When phosphorus levels are too low (hypophosphatemia), it can cause the softening and weakening of growing bones in children (rickets) and of mature bones in adults (osteomalacia).1

In children, XLH typically appears as bowed legs or knock knees. Over time, bone weakening can also lead to bone abnormalities in the legs, delayed growth, and short stature. In adults, XLH may cause osteomalacia, fractures and pseudo-fractures, and hypophosphatemia.1

About the XLH Disease Monitoring Program

The XLH DMP is an international, prospective, 10-year, longitudinal, observational study (NCT03651505) of adults and children with XLH in the US, Canada, and Latin America designed to characterize XLH disease presentation and progression, and prospectively assess changes over time in biochemical, clinical, and patient/caregiver-reported outcomes in a representative population. The program steering committee includes clinical experts in XLH, patient advocates from the XLH Network, and representatives from Kyowa Kirin and Ultragenyx Pharmaceutical.

About Kyowa Kirin

Kyowa Kirin aims to discover novel medicines with life-changing value. As a Japan-based Global Specialty Pharmaceutical Company, we have invested in drug discovery and biotechnology innovation for more than 70 years and are currently working to engineer the next generation of antibodies and cell and gene therapies with the potential to help patients with high unmet medical needs, such as bone & mineral, intractable hematological diseases/hemato-oncology, and rare diseases. A shared commitment to our values, to sustainable growth, and to making people smile unites Kyowa Kirin across the globe.

You can learn more about the business of Kyowa Kirin at: https://www.kyowakirin.com

Contact:
Susan Thiele
Head of Therapeutic Communications, North America
media.northamerica.bt@kyowakirin.com