FDA approves new drug Crysvita for rare bone diseases in children and adults.

The FDA has approved a new drug called Crysvita (burosumab) for two rare conditions that cause low phosphate levels in the blood: X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO). XLH is a genetic disorder that leads to soft, weak bones and growth problems in children. TIO is caused by certain tumors that make too much of a protein called FGF23, which causes the kidneys to waste phosphate. Crysvita is a monoclonal antibody that blocks FGF23, helping the body keep more phosphate. It is the first treatment to target the root cause of these diseases. Crysvita is approved for adults and children ages 6 months and older with XLH, and for patients ages 2 years and older with TIO whose tumors cannot be fully removed or found. Before starting Crysvita, patients must stop taking oral phosphate and active vitamin D supplements. Doctors will check blood phosphate levels before and during treatment to adjust the dose and avoid too much phosphate. This approval gives patients a new option, but it is not a cure. Patients should talk to their doctor to see if Crysvita is appropriate for their specific condition and to understand the risks and benefits.