Sierra Smith was driving with her sleeping toddler when she laughed — and her son startled awake. Travis, born profoundly deaf, had never reacted to sound. Three months after receiving an experimental gene therapy, he was hearing the world for the first time.

“That was like the most surreal moment a mother can feel when your son first hears your voice,” Smith told NPR.

On Thursday, the treatment that gave Travis his hearing became the first gene therapy for deafness to win FDA approval. The drug, called Otarmeni, is also the first gene therapy ever to restore a human sense — and Regeneron Pharmaceuticals says it will provide it for free in the US.

The molecular mechanics

The therapy targets an ultra-rare condition caused by mutations in the OTOF gene, which provides instructions for making a protein called otoferlin. In the cochlea — the snail-shaped structure in the inner ear — otoferlin acts as a critical relay, helping translate sound waves into electrical signals that reach the brain. Without it, the hair cells that detect sound remain intact, but the signal never gets delivered. The ear hears; the brain doesn’t.

Otarmeni loads a functional copy of the OTOF gene into a modified, harmless virus. Because the gene is too large for a single viral shell, researchers split it in half and packed it into two separate adeno-associated viruses. Surgeons make a small incision behind the ear, open a tiny hole in the skull, and infuse billions of these viruses directly into the cochlea. Once inside the hair cells, the two halves reassemble and begin producing otoferlin — restoring the connection between ear and brain.

Eighty percent improved, 42 percent heard whispers

The FDA’s decision rests on the CHORD trial, a study of 20 patients aged 10 months to 16 years, all born with severe-to-profound deafness from OTOF mutations. All had no measurable hearing at baseline.

Eighty percent — 16 children — achieved significant hearing improvement by 24 weeks. Among those followed to 48 weeks, every responder maintained their gains, and 42 percent reached normal hearing, including the ability to hear whispers.

“It’s miraculous,” Kerri, the mother of a 2-year-old trial participant named Miles, told CNN. “You go from being told your child’s profoundly deaf and may only ever hear with technology to your child’s hearing right alongside his friends.”

Common side effects — middle ear infection, nausea, dizziness, procedural pain — were broadly consistent with the surgery itself. The FDA approved Otarmeni in just 61 days, tied for the fastest biologics approval in modern agency history, under its National Priority Voucher pilot program.

Free — but only in the US

One-time gene therapies for rare diseases routinely carry seven-figure price tags. Regeneron chose a different path.

“We want to make an example of how science, and in this case biotech, can really deliver a gift to people — in this case, the gift of hearing,” Regeneron co-founder Dr. George Yancopoulos told CNN.

The company plans to seek regulatory approval in other countries but has not said whether the free-pricing model will extend beyond US borders. Patients may still face costs for the surgical procedure itself, which Regeneron does not perform.

What this means for gene therapy

OTOF-related deafness affects roughly 50 newborns per year in the US — a vanishingly small population. But the approval’s significance extends further. Gene therapy has largely proven itself in blood disorders: sickle cell, beta-thalassemia, hemophilia. Otarmeni is the first approved therapy to restore a neurosensory function to normal levels.

The approach could be adapted for other forms of genetic deafness. Researchers are already working on therapies targeting GJB2, the most common gene responsible for inherited hearing loss.

Zheng-Yi Chen, a Harvard Medical School associate professor at Mass Eye and Ear who was not involved in Regeneron’s trial, called the approval “an historical event, a landmark, a great development for the whole field” in an interview with NPR.

“We have been working in this field for decades and there was nothing, nothing, nothing,” Chen told the Harvard Gazette. “Then the treatment came out, worked really well, and now more trials are coming.”

A cultural tension

The approval also arrives inside a cultural conversation. Jaipreet Virdi, a historian of medicine and deafness at the University of Victoria who is deaf, told NPR that such therapies “reinforce this idea of deafness being a problem in need of eradication.”

“We’re saying: ‘Oh, deafness is a problem and we must fix that,’” Virdi said.

That tension — between a genuine medical advance and the lived experience of Deaf culture — won’t be resolved by any single drug. For families like Sierra Smith’s, the choice was personal.

“It’s incredible. Now he can hear me tell him how much I love him,” Smith said. “He knows has a name now. And he’s discovering all these different sounds.”

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