A new form of genetic therapy gives hope to people born with conditions affecting hearing and balance. Researchers from Massachusetts General Hospital and Harvard Medical School succeeded in restoring partial hearing and balance in mice. They used a method to deliver genes in the hair cells of the inner ear of mice.
Hair cells are delicate sensors in the inner ear which capture sounds and convert them to neural signals. Previously, these cells are difficult to treat however, the new form of gene delivery therapy can successfully access these hair cells. This advancement is important to those born with hearing impairment. One in 1000 babies every year are born with hearing impairment.
In a study published in Molecular Therapy, researchers detailed their method of gene delivery to inner-ear hair cells using exosome adeno-associated virus (AAV). With this technique, mice which were completely deaf were able to hear sounds equivalent of a loud conversation. It also improved its sense of balance.
"To treat most forms of hearing loss, we need to find a delivery mechanism that works for all types of hair cells," neurobiologist David Corey said according to Science Daily. Using exosomes or virus wrapped in protective bubbles, researchers super-charge the AAV which serves as a gene carrier to the inner ear. The exo-AAV can bind to the surface of the hair cells easier and can penetrate it more efficiently. A lab dish experiment revealed that AAV can only reach 20 percent of the hair cells. Meanwhile, exo-AAV successfully penetrated up to 50-60 percent of the hair cells.
The researchers tested the technique on mice who cannot hear even the loudest sounds and has poor balance. Their findings revealed that the gene therapy penetrated about 30 to 70 percent of the hair cells. Nine of 12 mice exhibited better balance and could get startled with a loud clap. Meanwhile, four could hear sounds measuring about 70 to 80 decibels which is equivalent to loud conversation. They added that the method might be years away before it can be used in humans. However, it gives hope to restore hearing of people with both genetic or acquired hearing impairment.
