Why Ultragenyx Pharmaceutical Inc. Shares Briefly Spiked Higher

Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Ultragenyx Pharmaceutical , a clinical-stage biopharmaceutical company focused on developing therapies to treat rare and ultra-rare diseases (as its stock symbol would imply), briefly shot higher by as much as 11% after announcing the results from a phase 1/2 study of investigational, subcutaneous anti-FGF23 monoclonal antibody KRN23 as a treatment for X-linked hypophosphatemia (an inherited metabolic bone disease) in adults. Shares have since retraced to a modest 2% gain.

So what: The trial, which was conducted by Kyowa Hakko Kirin Pharma, consisted of four escalating doses and was completed in 28 adult XLH patients. Injections were administered once every four weeks. As noted in Ultragenyx's press release, "The efficacy data from the Phase 1/2 study demonstrate that blocking excess FGF23 increases urinary phosphorus reabsorption, serum phosphorus levels, and 1,25 dihydroxy vitamin D levels. Repeat doses with KRN23 over four months led to an increase in serum phosphorus in 100% of patients, with approximately 89% of patients reaching the low end of the normal range." The key point there being that all patients experienced an increase in serum phosphorous, potentially implying a positive biologic effect on all stages of the diseases.

In addition, increases in bone remodeling marker P1NP were also statistically significant. Based on these results both Ultragenyx and Kyowa Hakko Kirin Pharma plan to initiate a pediatric phase 1/2 study this year and continue to develop KRN23 for adult XLH patients.

Now what: Although this is highly encouraging data and the market for orphan drug and ultra-orphan drugs can lead to hefty margins and high drug price tags, I'm not so certain that a $1.4 billion price tag isn't a bit frothy for a company that's wholly clinical. Note, that this doesn't mean Ultragenyx's therapies have given me any indication that they won't succeed, because today's results were definitely promising. However, I am implying that waiting for a larger data pool of patients might be wise with only six early stage clinical products in development.