The U.S. Food and Drug Administration today approved Crysvita (Burosumab), the first drug approved to treat adults and children ages 1 year and older with x-linked hypophosphatemia (XLH), a rare, inherited form of rickets. XLH causes low levels of phosphorus in the blood. It leads to impaired bone growth and development in children and adolescents and problems with bone mineralization throughout a patient’s life. Source 3n.