Drug developer Spark Therapeutics said Thursday that it had completed its biologics license application submission with the Food and Drug Administration for its experimental gene therapy for patients with rare inherited blindness.

If approved by the FDA, Spark's lead drug candidate, voretigene neparvovec, could be the first U.S. treatment that uses genes as medicine.

The Philadelphia biotech, spun out of Children's Hospital of Philadelphia, said the FDA will have 60 days to determine whether the application is complete. If the FDA decides the treatment should be given "priority review," that would set a six-month target review period, said company spokeswoman Monique da Silva. "The review period is still to be determined."

The gene therapy has received orphan, or rare-drug, designation in the United States and Europe. Companies that pursue a cure or treatment for a specific condition that affects a small percentage of the population — fewer than 200,000 in the United States — can receive tax reductions and an exclusive right to develop the medicine for seven years.

Spark's gene therapy also received "breakthrough therapy" designation by the FDA because it treats a serious or life-threatening disease or condition. The FDA will expedite the development and review of drugs designated as breakthrough therapies.

Spark's regulatory application includes data from three clinical trials that enrolled 41 participants. The therapy injects genes directly into the retina of the eye.

"We look forward to working closely with the FDA, with the hope of bringing voretigene neparvovec, the first potential gene therapy for a genetic disease in the U.S., to patients as quickly as possible," said Jeffrey D. Marrazzo, chief executive officer.

Spark, spun out of decades of research led by Katherine A. High at Children's Hospital, is also developing treatments for hemophilia and for an inherited retinal disease, choroideremia, that usually manifests during childhood in males as night blindness and a reduction of visual field.