Spark Therapeutics $ONCE  has scored an historic FDA approval of Luxturna, the world’s first such AAV-delivered gene therapy designed to cure a rare eye disease triggered by a genetic mutation.

The drug is OK’d for RPE65 mutation linked retinal dystrophy. The treatment uses a viral vector to insert the correct copy of a gene retinal cells need to create a protein that turns light into electric signals which can restore vision lost to the disease.

As with the earlier pioneering approval of the world’s first CAR-T, FDA commissioner Scott Gottlieb did the honors in recognizing the importance of this approval. And he says the agency will make sure that the regulatory path is straight and clear for the rest of the field looking to following Spark’s footsteps.

“We’re at a turning point when it comes to this novel form of therapy and at the FDA, we’re focused on establishing the right policy framework to capitalize on this scientific opening,” Gottlieb noted. “Next year, we’ll begin issuing a suite of disease-specific guidance documents on the development of specific gene therapy products to lay out modern and more efficient parameters — including new clinical measures — for the evaluation and review of gene therapy for different high-priority diseases where the platform is being targeted.”

“This one-time gene therapy for an inherited disease represents a first-of-its-kind breakthrough that may lay the groundwork for the development of gene therapies for other conditions that are not adequately addressed today,” said Jeffrey Marrazzo, CEO at Spark Therapeutics, in a statement. “We offer our sincere gratitude to the patients and their families as well as the expert investigators who continue to participate in Luxturna’s clinical development program.”

The next big step in this process? Marrazzo can tell us how much it will cost. The biotech has been hinting that the ticket will come in at about $1 million, stirring a long running debate over a new kind of drug designed to last a lifetime, but proven to work for only a limited amount of time.

Peak sales estimates tend to hover around the $500 million a year mark.

A Spark spokesperson said the company wouldn’t release the drug’s price until January, but that Luxturna is expected to be available in select treatment centers in Q1 2018.

Spark also has a closely watched hemophilia B gene therapy in the clinic, though its mixed data from their hemophilia A program underscored how many hurdles are left for the lead developers in the field.

The approval marks yet another quick decision for the FDA, which had a PDUFA date for this treatment in mid-January. This marks the 44th new drug approval for the year, just one shy of the mark hit in 2015. And the agency seems determined to hit that goal post, if not surge past.