According to a story from globenewswire.com, the pharmaceutical companies Ultragenyx and Kyowa Kirin recently issued an announcement that the U.S. FDA has granted approval to their new treatment Crysvita (burosumab-twza). This drug was developed for the treatment of X-linked hypophosphatemia is both pediatric and adult patients. The approval of Crysvita is a significant innovation for patients suffering from this condition, who now will have a treatment option that helps address the underlying disease mechanism.
Hypophosphatemia is a term that can describe any form of electrolyte disturbance in which there is an unusually low amount of phosphate in the blood. X-linked hypophosphatemia (XLH) is a distinct, genetically linked form that manifests as a variation of rickets, a disease that causes soft and weak bones in children. Unlike most cases of rickets, vitamin D supplementation has little effect. X-linked hypophosphatemia can cause symptoms such as hearing loss, osteoarthritis, bone pain, and skeletal abnormalities. The condition also causes distinct changes to the dentition, such as tooth abscesses, an enlarged pulp chamber, and interglobular dentin. The disease prevents the kidneys from reabsorbing phosphate back into the bloodstream, which causes the low concentrations. While there are treatments available that can address some symptoms, such as the characteristic bow legged stance common in rickets, Crysvita is the first option that aims to address the underlying disease. To learn more about X-linked hypophosphatemia, click here.
Crysvita displays a unique mechanism of action. It is an antibody that modulates the action of fibroblast growth factor 23 (FGF23). FGF23 is released in excessive amounts in people with XLH and it is responsible for the phosphate wasting that occurs in the condition. Instead of being reabsorbed, phosphate is lost in the urine, and the growth factor also impacts the ability of the kidneys to produce active vitamin D. By normalizing the impact of FGF23, Crysvita is able to regulate phosphate concentrations to normal levels and improve bone mineralization. This strengthens the bones overall and reduces the chance of breakage, which is a significant risk in rickets.
