FDA approves first drug for rare form of rickets: 3 things to know

The FDA approved Ultragenyx Pharmaceutical's drug Crysvita April 17 to treat patients with a rare, inherited form of rickets known as x-linked hypophosphatemia.

Here are three things to know.

1. XLH, which causes low phosphorous levels in the blood, leads to impaired bone growth in children and issues with bone mineralization in adults.

2. In a recent clinical trial, a majority of patients (94 percent) demonstrated normal phosphorus levels after taking Crysvita once a month, compared to just 8 percent of patients taking a placebo.

"XLH differs from other forms of rickets in that vitamin D therapy is not effective," said Julie Beitz, MD, director of the Office of Drug Evaluation III in the FDA's Center for Drug Evaluation and Research. "This is the first FDA-approved medication for the treatment of XLH and a real breakthrough for those living with this serious disease."

3. The FDA granted both a breakthrough therapy designation and an orphan drug designation for Crysvita.