The US Food and Drug Administration (FDA) on Tuesday approved a new gene therapy from Spark Therapeutics for the treatment of children and adult patients with an inherited form of vision loss that may result in blindness.

The approval comes two months and a week after an advisory committee of outside experts unanimously voted in favor of approving the treatment for the condition which affects about 6,000 worldwide. The price of the new gene therapy, which Leerink analysts have said could cost $600,000 per patient in the US and $400,000 in the EU, is not expected to be revealed until next month and the treatment is not expected to be available until late in the first quarter of 2018.

“Today’s approval marks another first in the field of gene therapy — both in how the therapy works and in expanding the use of gene therapy beyond the treatment of cancer to the treatment of vision loss — and this milestone reinforces the potential of this breakthrough approach in treating a wide-range of challenging diseases,” FDA Commissioner Scott Gottlieb said in a statement.

FDA granted Luxturna's application priority review, breakthrough therapy and orphan designations. In addition, because of the approval, Spark receieved a rare pediatric priority review voucher (PRV), the 13th rare pediatric PRV issued by FDA since the program began.

To further evaluate the therapy's long-term safety, Spark plans to conduct a post-marketing observational study involving patients treated with Luxturna.

The approval caps a big year for the approval of cell and gene therapies. Two CAR-T cell therapies were also approved in 2017: Novartis' Kymriah (tisagenlecleucel) in August for certain pediatric and young adult patients with a form of acute lymphoblastic leukemia and Gilead’s CAR-T therapy Yescarta (axicabtagene ciloleucel) to treat adult patients with certain types of large B-cell lymphoma who have not responded to or who have relapsed after at least two other kinds of treatment.