Thanks to gene therapy, a number of children who were born with inherited deafness can now hear.

A recent study, released on Wednesday, reports significant improvement in hearing for five out of six children who received treatment in China. Another study, released by the Children’s Hospital of Philadelphia on Tuesday, also shows similar improvements in an 11-year-old boy who was treated there. Additionally, Chinese researchers published a study earlier this month demonstrating similar results in two other children.

At this point, the experimental treatments are focused on a single uncommon condition. However, researchers believe that these same therapies could potentially be beneficial for numerous children who have different forms of deafness caused by genetic factors. Worldwide, approximately 34 million children experience deafness or hearing impairment, with genes accounting for up to 60% of cases. Gene therapy, which has already been authorized to treat conditions like sickle cell disease and severe hemophilia, is now being utilized to address hereditary deafness.

Children who have inherited deafness commonly receive a cochlear implant, a device that aids in their ability to hear sound.

Zheng-Yi Chen, a senior author of the study published in the journal Lancet, expressed that despite previous efforts to find a solution, no treatment has been able to reverse hearing loss. He stated, “That’s why we have been continuously working towards developing a therapy.” Chen also shared his joy and excitement about the positive results of the study.

The team recorded videos to track the progress of patients. In one video, a baby who was previously unable to hear can be seen looking back in response to a doctor’s words six weeks after treatment. In another video, a young girl can be seen 13 weeks after treatment repeating words such as father, mother, grandmother, sister, and “I love you.”

All of the kids involved in the trials have a specific condition that makes up 2% to 8% of inherited hearing loss. This is due to changes in a gene that produces a protein in the inner ear called otoferlin, which aids in the transmission of sound from hair cells to the brain. The treatment involves surgically introducing a working version of this gene to the inner ear in a single session. While most of the children received treatment in one ear, one child in the two-person study had both ears treated.

Six children were involved in the study at Fudan University in Shanghai, which was co-led by Dr. Yilai Shu, a member of Chen’s lab and a collaborator on the research. The study was funded by Chinese science organizations and biotech company Shanghai Refreshgene Therapeutics.

The children were studied for approximately six months. The reason for the treatment’s failure in one child remains unknown. However, the remaining five, who were previously completely deaf, are now able to engage in regular conversations and communicate with others. It is estimated that they can hear at about 60% to 70% of the normal level. There were no significant side effects from the therapy.

Initial findings from other investigations have yielded similarly favorable outcomes. In October, Regeneron Pharmaceuticals of New York announced that a child under the age of 2 in a study they funded with Decibel Therapeutics displayed improvements six weeks after receiving gene therapy. One of the testing locations, a hospital in Philadelphia, reported that their patient, Aissam Dam of Spain, experienced hearing for the first time after undergoing treatment in October. Although the sounds are still muffled, as if he is wearing earplugs, he is now able to hear his father’s voice and sounds from passing vehicles, according to Dr. John Germiller, who oversaw the research in Philadelphia.

The improvement was quite significant, according to Germiller. He explained that the individual went from experiencing total and severe hearing loss with no ability to perceive sound to a state of mild to moderate hearing impairment, which is considered a mild disability. This progress is thrilling for both us and the individual involved.

Dr. Lawrence Lustig of Columbia University, who is participating in the Regeneron trial, stated that while the children involved in these studies do not achieve perfect hearing, even a moderate improvement in their hearing loss is remarkable.

However, he stated that there are still many unanswered questions, including the duration of the therapies and the potential for continued improvement in the children’s hearing abilities.

There is debate over the ethical implications of using gene therapy to treat deafness. Teresa Blankmeyer Burke, a philosophy professor and bioethicist at Gallaudet University who is deaf herself, stated that there is no agreement on whether gene therapy for deafness is necessary. She also noted that deafness is not a life-threatening condition like sickle cell disease. She emphasized the importance of consulting with members of the deaf community when considering the use of gene therapy, as it could be seen as a threat to the thriving of deaf communities that use sign language as their primary means of communication.

In the meantime, the researchers reported that their progress is continuing.

Chen stated that this serves as tangible evidence of the effectiveness of gene therapy. It also signals the potential for advancements in the entire field.

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