Ultragenyx and Kyowa Kirin Announce Topline Phase 3 Study Results Demonstrating Superiority of Crysvita® (burosumab) Treatment to Oral Phosphate and Active Vitamin D in Children with X-Linked Hypopho

Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE), a biopharmaceutical company focused on the development of novel products for rare and ultra-rare diseases, Kyowa Hakko Kirin Co. Ltd (Kyowa Hakko Kirin), and Kyowa Kirin International PLC (Kyowa Kirin International) today announced that the Phase 3 study of Crysvita® (burosumab) met its primary endpoint demonstrating that Crysvita was superior to oral phosphate and active vitamin D (conventional therapy) in improving rickets in children with X-linked hypophosphatemia (XLH) after 40 weeks of treatment (LS Mean treatment difference  of +1.14, p<0.0001). The study also showed improvement in important metabolic and functional measures with Crysvita treatment, and a safety profile similar to that observed in other Crysvita pediatric XLH studies. Crysvita is an antibody that blocks fibroblast growth factor 23 (FGF23), a hormone that causes phosphate urinary excretion and suppresses active vitamin D production by the kidney.

“This is the first study that directly compares Crysvita to conventional therapy for XLH, and we have now clearly demonstrated that Crysvita has a rapid and profound effect on the underlying disease, an outcome that was not achieved with conventional therapy,” said Camille L. Bedrosian, M.D. Chief Medical Officer of Ultragenyx. “These data reinforce the results seen in our earlier Phase 2 studies, and we believe that Crysvita will transform the treatment of XLH in children.”

“The results of this important controlled study demonstrate the value of directing therapy at the mechanism of renal phosphate wasting in XLH,” said the lead study investigator, Erik Imel, M.D., Associate Professor of Medicine and Pediatrics at Indiana University School of Medicine. “While prior conventional therapy fails to improve renal phosphate wasting, Crysvita works to improve serum phosphorus by correcting the renal phosphate wasting. The differences in mechanism are clearly important to outcomes as demonstrated in this study. By comparing XLH patients treated with Crysvita to patients treated with conventional therapy, we are finally able to demonstrate the magnitude of benefit on parameters of serum phosphorus, bone metabolism, and improvements in the skeleton.”

“I am pleased that the study provides valuable data for pediatric patients with XLH,” said Mitsuo Satoh, Executive Officer, Vice President Head of Research and Development Division of Kyowa Hakko Kirin. “I believe Crysvita has the potential to be an effective treatment option for patients with XLH.”