Ultragenyx Pharmaceutical has received "Breakthrough Therapy" designation from the U.S. Food and Drug Administration (FDA) for KRN23 for treatment of XLH in pediatric patients. http://ir.ultragenyx.com/releasedetail.cfm?ReleaseID=977346
This is not the same as getting FDA approval to make the drug available to patients outside a clinical setting, but it is an acknowledgment that KRN23 is the first potential treatment option in development for patients with XLH. The designation is intended to expedite the development and review process when the preliminary clinical evidence indicates that the treatment may demonstrate substantial improvement over existing therapies.
Getting this designation is encouraging news, since it removes some of the delays inherent in governmental reviews, while still providing for patient safety by carefully weighing the benefits and risks.