Ultragenyx sees positive signs in rickets study

NOVATO -- Ultragenyx (Nasdaq: RARE), a biotechnology company based in Novato, on Monday said it has positive early results from a long-term study of its KRN23 drug for adults with inherited rickets, a bone disease that leads to bone pain, bowed legs, impaired growth, osteoarthritis and other maladies.

There are an estimated 3,000 pediatric and 9,000 adult patients in the U.S. with the disease.

Inherited rickets is also called XLH, or X-linked hypophosphatemia. Patients with XLH have low phosphate levels in their blood, caused by excess phosphate loss into the urine, which itself is caused by the effect on kidney function of excess fibroblast growth factor 23 (FGF23) production in bone cells.

All patients in the study continued to demonstrate increases in serum phosphorus and the most maintained levels in the normal range, according to Ultragenyx.

"By binding and inhibiting FGF23, patients treated with KRN23 demonstrated increases in phosphate levels over the cumulative 16-month treatment period," said Sunil Agarwal, M.D., chief medical officer of Ultragenyx. "Based on these encouraging results, we plan to continue development in adult XLH patients and are enrolling pediatric XLH patients in our ongoing phase 2 study."

FGF23 is produced by cells responsible for bone formation to manage calcification as part of bone growth by prompting the kidneys to excrete phosphate and reduce production of vitamin D when phosphate levels are too high. Low phosphate levels result in insufficient bone mineralization.

There is no approved drug therapy or treatment for the underlying cause of XLH. Most patients are managed using oral phosphate replacement and vitamin D therapy, which helps restore bone growth but has significant side effects. The therapies require close monitoring because spikes in phosphate levels can severely damage the kidneys.

KRN23 is a human monoclonal antibody, injected under the skin, that helps to bind and reduce the biological activity of FGF23 to increase abnormally low phosphate levels in patients with XLH.

The Ultragenyx CEO is Emil Kakkis. Founded in 2010, it is a clinical-stage company that seeks treatment for rare and diseases, especially genetic diseases.

With an hour left in the Monday trading session, Ultragenyx's stock price was $56.80, down nearly 2 percent from Friday.

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