On Tuesday, a US Food and Drug Administration review committee published a document signaling that a historic moment in medicine may be on the horizon. The committee found that an experimental gene therapy for a rare inherited form of blindness improves vision, at least in the short term. If approved, the technique would be the first gene therapy for an inherited disease approved in the United States.

The review of the drug, Luxturna, from Spark Therapeutics, comes two days before a key meeting of outside experts who will recommend to the FDA whether the drug should be approved. Importantly, the reviewers note that the drug meets criteria for approval.

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In a key study of 21 patients with an inherited blindness condition known as Leber congenital aumaurosis—a condition triggered by mutations to the RPE65 gene—11 patients who underwent the experimental treatment experienced significant vision improvement. In addition, 93 percent of participants experienced at least some improvement. Improvement here was measured by an ability to navigate obstacles under poor lighting conditions. The drug works by delivering a correct copy of the RP65 gene to retinal cells, restoring a person’s ability to produce the deficient enzyme that causes the condition. The details of this work have been published in The Lancet.

But the review also notes that there is no long-term data. On Thursday, the panel will consider the possibility that patients may need multiple treatments over time (Spark had billed this technique this as a “potential one-time treatment”). They will also consider that patients failed to achieve significant improvement in a more standard measure of vision, visual acuity.

If the drug is approved, Spark estimates that it may help between 1,000 and 2,000 people in the US with an inherited retinal disease caused by the RPE65 gene. The company has not disclosed how much the drug will cost, but like other gene therapies currently racing to market, it is likely to cost hundreds of thousands of dollars.

[FDA, The Lancet]