With the FDA approval of Luxturna in December 2017, Spark became the first biotech company to market a gene therapy to fix an inherited disorder, a form of congenital vision loss caused by a mutation in a gene called RPE65. Its treatment—priced at $425,000 per eye—involves injecting engineered virus particles directly into the retina. The virus particles contain a correct copy of the RPE65, which replaces the mutant version in the retinal cells, significantly improving the vision of patients in clinical trials. Several thousand people around the world likely be eligible for the treatment, but it could open the door for other gene therapies that may eventually treat many other mutations known to cause blindness. Luxturna is based on more than two decades of research at the Children’s Hospital of Philadelphia, which contributed $50 million to launch Spark in 2013. Spark will manufacture Luxturna at its own facility in West Philadelphia, and will train surgeons to administer the treatment at selected U.S. locations.