LONDON — A baby girl born with profound genetic deafness can now hear unaided after receiving a “groundbreaking” gene therapy trial, Britain’s National Health Service said Thursday.

Opal Sandy, an 18-month-old from Oxfordshire, England, is the first patient treated in a global gene therapy trial that is showing “mind-blowing” results, Addenbrooke’s Hospital in Cambridge said in a statement. Opal is “the first British patient in the world and the youngest child to receive this type of treatment,” the hospital said.

The treatment is already having practical results, the hospital said: Opal can now respond to her parents’ voices and can communicate words such as “Dada” and “bye-bye.”

“When Opal could first hear us clapping unaided it was mind-blowing,” her mother, Jo Sandy, said in a statement. “We were so happy when the clinical team confirmed at 24 weeks that her hearing was also picking up softer sounds and speech.”

Her father, James Sandy, said that it was “already making a difference to our day-to-day lives, like at bath-time or swimming. … We feel so proud to have contributed to such pivotal findings, which will hopefully help other children like Opal and their families in the future.”

The results are another example of the potential of gene therapies, which use the insertion of genetic material to treat diseases.

Opal, like her elder sister, was born deaf because of a rare genetic condition known as auditory neuropathy, which is caused by the disruption of nerve impulses traveling from the inner ear to the brain, the hospital said. However, within four weeks of having the gene therapy infusion to her right ear, Opal “responded to sound,” it added. Now, at 24 weeks after treatment, clinicians have been able to confirm “close to normal hearing levels for soft sounds,” even including “whispering, in her treated ear.”

Manohar Bance, chief investigator of the trial and an ear surgeon at Cambridge University Hospitals NHS Foundation Trust, said the results were “spectacular and better than I expected.”

“This is hopefully the start of a new era for gene therapies for the inner ear and many types of hearing loss,” he said.

Auditory neuropathy can be due to a variation in a gene, known as the OTOF gene, which produces a protein needed to allow the inner hair cells in the ear to communicate with the hearing nerve. According to the NHS, about 20,000 people across Britain, Germany, France, Spain and Italy are deaf because of a mutation in the OTOF gene.

This type of hearing loss is not commonly detected until children are about 2 or 3 years of age, when a delay in speech is likely to be noticed, the Cambridge hospital said. However, Opal’s was detected earlier, when she was just 3 weeks old, as her older sister also has the same genetic condition.

The trial that Opal was a part of began in May last year and was sponsored by U.S. biotechnology company Regeneron. It is continuing to enroll patients in the study in the U.S., Britain and Spain, it said.

The procedure involved Opal being given an infusion via an injection into her right cochlea during surgery, containing a modified virus known as AAV1, which acts as a “working copy of the OTOF gene.” A cochlear implant was also fitted at the same time to her left ear.

Congenital deafness – hearing loss present at birth – is a “significant unmet medical need that affects approximately 1.7 out of every 1,000 children born” in the United States, according to Regeneron.

“While hearing aids and cochlear implants can amplify sound to improve hearing for individuals with a range of hearing loss, these devices do not currently restore the full spectrum of sound,” it added.

The news has been welcomed in Britain, making national headlines, but it could have a global impact.

“Many families will welcome these developments, and we look forward to learning about the long-term outcomes for the children treated,” Martin McLean of Britain’s National Deaf Children’s Society said in an emailed statement Thursday. “This trial will teach us more about the effectiveness of gene therapy in those cases where deafness has a specific genetic cause.”

The trial was expected to include up to 18 children from Britain, the U.S. and Spain, the hospital said in a statement when the trial began last year. Their progress will be followed for up to five years to see the extent to which their hearing improves.

Other clinical trials looking into gene therapies as a way to restore hearing in children with deafness caused by OTOF gene variations are also underway elsewhere in the world. Last year, an 11-year-old boy, Aissam Dam, received treatment in a separate gene therapy trial at the Children’s Hospital of Philadelphia. China is also conducting a number of trials.

Opal’s tentatively successful results at 24 weeks after treatment, along with other scientific data from the trial, are set to be presented at the annual meeting of the American Society of Gene and Cell Therapy in Baltimore this week.

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