US health officials have approved the nation's first gene therapy that improves the sight of patients with a rare form of inherited blindness.
The approval for Spark Therapeutics offers a life-changing intervention for a small group of patients with a vision-destroying genetic mutation and hope for many more people with other inherited diseases.
The drug maker said it will not disclose the price until next month, delaying debate about the affordability of a treatment that analysts predict will be priced around $US1 million ($A1.4 million).
The injection, called Luxturna, is the first gene therapy approved by the Food and Drug Administration for an inherited disease and the first in which a corrective gene is given directly to patients. The gene mutation interferes with the production of an enzyme needed for normal vision.
Patients who got the treatment have described seeing snow, stars or the moon for the first time.
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Luxturna is delivered via two injections - one for each eye - that replaces the defective gene that prevents the retina, tissue at the back of the eye, from converting light into electronic signals sent to the brain.
The FDA has approved three gene therapies since August, as decades of research into the genetic building blocks of life begin translating into marketable treatments. The previous two are custom-made treatments for forms of blood cancer.
Novartis' Kymriah is priced at $US475,000 for a one-time infusion of genetically enhanced cells. Gilead Sciences' similar treatment, Yescarta, costs $US373,000 per treatment.
