Spark Therapeutics Inc’s experimental gene therapy for a rare form of blindness improves vision and should be approved, advisers to the Food and Drug Administration concluded on Thursday, paving the way for the first U.S. gene therapy for an inherited disease.

FILE PHOTO: A view shows the U.S. Food and Drug Administration (FDA) headquarters in Silver Spring, Maryland August 14, 2012.

The panel voted unanimously in favor of the treatment, Luxturna, which is designed to treat inherited retinal diseases caused by defects in a gene known as RPE65, which tells cells to produce an enzyme critical to normal vision.

The FDA is not obliged to follow the recommendations of its advisers but typically does. Michael Yee, an analyst at Jefferies, said in a recent research report that approval of the therapy would “thematically mark a watershed moment for the entire field.”

The panel’s vote followed scientific presentations from Spark and the FDA and testimonies from patients who described the impact of the therapy, such as allowing them for the first time to see the moon and stars, go out with friends at night, and see food on their plate. The agency is due to makes its decision by Jan. 12, 2018.

Jeffrey Marrazzo, Spark’s chief executive, declined in a recent interview to say what the company would charge for the treatment. He said one benchmark would be the price of drugs for other ultra-rare diseases such as Pompe disease, Hunter Syndrome and paroxysmal nocturnal hemoglobinuria, which can range from $300,000 a year to $600,000 a year or more.

If approved, analysts expect Luxturna to generate annual sales of more than $400 million by 2021. The company’s shares have risen 160 percent over the past 12 months, reaching a high of $91.00 on Sept. 29, amid optimism the product would be approved. They were halted during the committee meeting.

Retinal disease caused by defects to the RPE gene affect between 1,000 and 2,000 people in the United States. Roughly half of those become legally blind by the age of 16 and all are legally blind by the age of 34. Most progress to complete blindness.

Legal blindness refers to people whose vision is 20/200 or less. A person with normal vision can see an object 200 feet away. A legally blind person must stand 20 feet in front of it. People who are completely blind cannot see any light or shapes.

Clinical trial results showed 93 percent of participants experienced some improvement in their functional vision as measured by their ability to navigate obstacles in poor light.

Source: Reuters