Estimated to be about 35-55% of all age-related hearing loss cases, genetic hereditary hearing loss is more common than you may think, and even more confounding to the medical community. Caused by a myriad of genetic mutations ranging from disorders to ear deformation at birth, the exact genetic reason may be difficult to pinpoint in patients, but a new study conducted by a joint team of scientists at Harvard Medical School and Boston Children’s Hospital is bringing new hope to those suffering from hereditary hearing loss. By utilizing a refined gene-editing system, researchers have found promising results by restoring the hearing of “Beethoven” mice, which carry the genetic mutation responsible for profound hearing loss.
Hereditary hearing loss is a hearing loss caused by genetic mutations or factors that make patients more predisposed to hearing loss. Certain genes may make patients more susceptible to hearing loss from aging, or induced by noise, drugs, and infections, than others without similar genetic makeups, proving that hearing loss, or disorders such as Otosclerosis, Usher’s syndrome, and Pendred syndrome that cause hearing impairments may be passed down through generations.
Gene mutations may also cause non-hearing related hereditary conditions, such as deformation of the inner ear, which in turn, can result in deafness at birth or later in life. These pediatric ear malformations are still not fully understood, further adding to the mystery behind hereditary hearing loss, but research indicates that genetic mutations or inherited conditions may be contributing factors. Unfortunately, for 48 million Americans with hearing loss, their hearing loss may be pre-determined even before birth.
Utilizing an optimized and more precise version of the CRISPR-Cas9 gene-editing system, the research team at Harvard Medical School and Boston Children’s Hospital were able to properly target the disease-causing genetic mutation responsible for hearing loss in “Beethoven” mice with impeccable accuracy. So accurate in fact, that their system had recognized a single incorrect DNA letter in the defective copy among 3 billion letters in the mouse genome. With the ability to lock on to the defective copy of a hearing gene called Tmc1, the team was able to disable the defective copy while sparing the healthy copy, effectively “shutting off” the gene that causes hearing loss.
To ensure the therapy had worked in animals and not just cells, researchers measured the mice’s auditory brainstem responses, capturing how much sound is detected by sensory cells in the inner ear and sent to the brain. Two months after treatment, the mice could detect sounds reaching 45 decibels, 16 times the capability of untreated mice. Researchers were enthusiastic about these results, stating “the work represents a milestone because it greatly improves the efficacy and safety of standard gene-editing techniques.”, but remained cautious about using this technique on humans just yet. “Much more work remains to be done before even a highly precise gene-editing therapy like this one could be used in humans.”