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Here’s what you’ll learn when you read this story:
The majority of deafness cases throughout the world are genetic in origin, and for years, scientists have exploring ways that gene therapies could make deafness a thing of the past.
By delivering a functional version of the OTOF gene, which plays a big role in transmitting auditory signals from the ear to the brain, patients’ hearing drastically improved from perceptible sound decreasing from 106 decibels to just 52 decibels.
The OTOF gene was delivered via injection in the membrane at the base of the cochlea using an adeno-associated virus, or AAV, a well-tested and safe method for genetic therapies.
The world is filled with noises that can lead to permanent hearing loss. Just go to a rock concert for a few hours, and the resulting days-long tinnitus is enough anatomical evidence to prove the point. However, the majority of cases regarding hearing loss in children and adults comes from genetics, an unfortunate mutation somewhere in a person’s genome that interrupts the otherwise remarkable process of turning sound waves into electrical signals that can be interpreted by our brain (aka auditory transduction).
With the arrival of gene-editing tools, such as CRISPR, scientists have begun making strides to make hereditary deafness a thing of the past. However, as you might expect, achieving such a medical miracle isn’t easy. More than 120 genes have been linked to hearing loss, so isn’t like you can just flip a switch and fix the problem. Previous studies have analyzed different genes, including TMC1, Atp2b2, and others, typically on mouse models with positive results.
But a new study, analyzing the gene OTOF, tested its gene therapy on ten patients between the ages of 1 to 24 at five hospitals throughout China. The study, published in the journal Nature Medicine, detailed how all ten patients experienced vast hearing improvement with perceptible sound increasing from 106 decibels (which is about the equivalent of a car horn at close range) to 52 decibels—below the range of a typical conversation.
“This is a huge step forward in the genetic treatment of deafness, one that can be life-changing for children and adults,” Karolinska Institutet in Sweden’s Maoli Duan, a co-author of the study, said in a press statement. “Smaller studies in China have previously shown positive results in children, but this is the first time that the method has been tested in teenagers and adults, too.”
Researchers delivered the treatment via a synthetic adeno-associated virus, or AAV, a well-known vector for gene therapy as it can deliver DNA directly to targeted cells. The ability to generate these AAV particles so that they contain no viral genes but only DNA required for therapeutic intervention has made them one of the safest methods for gene therapies. Scientists then injected a functional version of the OTOF gene in the “round window,” a membrane at the base of the cochlea.
After a month of treatment, the patients were already showing signs of improvement, and six months later, they reported even greater auditory gains. While this was one of the first treatments on teenagers and adults—and all ages showed signs of improvement—the biggest gains were between the ages of five and eight. According to the researchers, one seven-year-old girl showed the greatest transformation, recovering nearly all of her hearing and holding daily conversations with her mother just four months later.
Although promising for this particular genetic mutation, scientists have a long way to go before they can confidently reverse genetic hearing loss across the board. In fact, targeting OTOF may have been one of the easier challenges when it comes to genetic therapies for hearing loss.
“OTOF is just the beginning,” Duan said in a press statement. “We and other researchers are expanding our work to other, more common genes that cause deafness, such as GJB2 and TMC1. These are more complicated to treat, but animal studies have so far returned promising results. We are confident that patients with different kinds of genetic deafness will one day be able to receive treatment.”
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