Shares of Spark Therapeutics (ONCE) ended the day up 25% after reporting positive phase 3 results in patients with rare blindness. More specifically these patients have a rare blindness that is caused by the RPE65 gene — also known as inherited retinal dystrophies. The company uses its gene therapy drug known as SPK-RPE65 to restore a gene that is defective back to its normal state. 

The company ran this phase 3 trial using SPK-RPE65 and comparing it to a placebo compound to determine functional vision improvement between baseline — starting at zero sum — and a one year time point. The SPK-RPE65 gene therapy drug showed greater improvement from baseline compared to the placebo compound, meeting the primary endpoint of the trial ,p-value of p = .001. The p-value is a standard measure in clinical trials to determine if the drug is statistically significant in using over a placebo compound.

In addition, there were two secondary endpoints that were statistically significant using the SPK-RPE65 gene therapy drug. Compared to placebo, full-field light sensitivity threshold improved, as did mobility test change score for first injected eye. The former achieved a p-value of p < .001 and the latter achieved a p-value of p = .001. A third secondary endpoint, visual acuity, did not show a statistically significant difference from placebo.

The gene therapy drug was safe and tolerable as there were no serious adverse events reported in the trial. In addition patients did not exhibit an immune response to the injected gene therapy drug allowing it to achieve proper efficacy. 

Today's results are a huge refresh for the gene therapy sector because of the two previous companies that failed to capitalize in this space. Both Celladon (CLDN) and Avalanche (AAVL) failed to achieve positive efficacy in their phase 2 trials, halting the progress of their respective drugs. Celladon failed to produce a gene therapy drug for heart failure and Avalanche failed to improve patients with macular degeneration.