What happened

Shares of Spark Therapeutics Inc. (NASDAQ:ONCE), a clinical-stage biotech developing gene therapies, rose 23.5% in August, according to data from S&P Global Market Intelligence. The company pleased investors with clinical trial data for a hemophilia drug in early stage development.

So what 

The FDA recently accepted the company's first new drug application that could make Luxturna an important option for patients with a rare gene mutation that leads to blindness. It might be a phase 1/2 study, but early results for hemophilia A candidate SPK-8011 suggests that more candidates emerging from Spark Therapeutics' proprietary discovery platform could reach the agency's inbox in the years ahead. 

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While winning an approval for Luxturna would be a huge accomplishment for Spark, hemophilia represents a much larger addressable patient population. So far, all three patients treated with SPK-8011 have begun producing significant amounts of the clotting factors they need on their own without showing any adverse side effects.

Now what

Recently launched treatments that replace enzymes hemophilia patients can't produce on their own have raised annual spending on hemophilia drugs to around $10 billion. Although there's a great deal of competition for hemophilia patients, SPK-8011 for hemophilia A, and SPK-9001 for hemophilia B, which is partnered with Pfizer, could quickly become market leaders, if the candidates can repeat the results like those reported last month.

The FDA is expected to announce an approval decision for Luxturna in January. Because it addresses a rare childhood disease, Spark is entitled to a priority review voucher that allows the bearer to shorten the review process of any submission. These transferable vouchers fetch hundreds of millions in the open market, which could go a long way toward developing the hemophilia game changers in its pipeline.