For the first time, people born with a rare, inherited form of deafness have a treatment option beyond hearing aids and cochlear implants.

That’s because, on Thursday, the Food and Drug Administration approved a one-off therapy designed to overcome the genetic hiccup that causes this hearing loss and offer a lasting fix. Developed by Regeneron Pharmaceuticals, the gene therapy has already shown great promise in the key clinical study supporting its approval.

“I’ve witnessed firsthand my trial participant responding to their mother’s voice, dancing to music and interacting with the world, and these moments are now possible for more children born with this specific form of hearing loss,” said Eliot Shearer, an investigator in that trial, in a statement from Regeneron.

The therapy, Otarmeni, is now cleared for use in children and adults who have severe-to-profound hearing loss because of variations in a gene known as OTOF. Such variations keep hairs in the inner ear from producing a protein that’s essential for relaying sound signals to the brain. Otarmeni is administered through a surgical process similar to that of cochlear implants, and uses a disarmed virus to smuggle into the inner ear a working copy of the defunct gene.

That key study recruited 20 children with OTOF hearing loss, who ranged in age from 10 months to 16 years and were given a dose of Otarmeni in either one or both ears. Four participants entered already having a cochlear implant in one ear, while some others got the devices as part of the experiment. The main goal was to see if Otarmeni could get hearing into the moderate to normal range.

Six months after treatment, 80% of participants had hit that benchmark. According to Regeneron, they could hear at least 70 decibels — the kind of sound one might expect from a loud conversation or a clamorous household appliance. Whether a patient was younger or older also didn’t seem to impact the therapy’s effectiveness, a result that likely influenced the FDA to include adults in the label.

“Is there really any difference between a 16- and a 21-year-old for something like this? We don't think so,” said Jonathan Whitton, Regeneron’s vice president of genetic medicines, in an interview. “It's a pleasant surprise for a lot of people in our field, me included, that it looks like the treatment window is so broad.”

In the trial, parents of the 10-month-old noticed changes within a few weeks. Their daughter started reacting to handclaps and became more aware of speech and whispers. Parents of a different young girl reported “spectacular” progress one year after treatment, as she could now respond to distant sounds and understand speech in noisy environments.

So far, Otarmeni also appears generally safe, with the most common adverse events being inner ear infections, vomiting, nausea, dizziness and procedural pain. Lawrence Lustig, another trial investigator, noted after a data release late last year how these events were mostly minor, short-lived and the type to be expected from any sort of ear-related surgery.

Otarmeni has “rapid, meaningful and consistent” effects, and its approval “signals a new era in the treatment of genetic forms of hearing loss, where reinstating 24/7 natural hearing is now possible,” added Shearer, who also serves as an otolaryngologist at Boston Children’s Hospital.

As with most cutting-edge medicines, there are still outstanding questions. Scientists aren’t entirely sure how long Otarmeni’s effects will last, or why it works better in some patients. At that earlier data cut, at least one participant didn’t have any significant hearing improvement. There, Whitton said none of the most likely causes have checked out. The leading hypothesis now, he said, is there was some kind of delivery issue, but “we don’t have definitive proof of that yet.”

Regeneron said it will provide Otarmeni at no cost to “clinically eligible individuals” in the U.S., though that doesn’t necessarily mean no out-of-pocket costs for administration. In the past, insurance companies have seriously weighed the benefit and durability of gene therapies, which often carry list prices into the hundreds of thousands — if not millions — of dollars.

“What we’re talking about, really, is: what’s the value of hearing?” Whitton said in a previous interview. “My expectation is most people see massive value, having hearing connect you to your environment, to others, to your families.”

Yet that value isn’t guaranteed to translate to commercial success. Very few people have OTOF-related hearing loss. The addressable population is further winnowed by the fact that Otarmeni can’t be administered to any ears that already have cochlear implants.

David Risinger, an analyst at the investment firm Leerink Partners, has also described a “crowded competitive landscape” in this area of drug development, with at least three companies, including Eli Lilly, advancing their own gene therapies.

Otarmeni received a lightning fast approval review thanks to a new and controversial voucher program recently enacted by the FDA. It's the first gene therapy with a “national priority” voucher to be OK'd for market.