Researchers used a small genetic patch to partially restore hearing and balance in deaf mice with Usher syndrome, according to a new report published in Nature Medicine.

The animal study, which is still in its early stages, could eventually develop into new treatments for Usher syndrome, a congenital hearing disorder which usually goes hand-in-hand with blindness as well.

When the scientists injected the profoundly deaf mice with the genetic patch, they developed into partially hearing mice with no balance problems.

The authors explained that deafness is the most common sensory disorder. Approximately 1 in every 1,000 newborns is born with a hearing impairment. Congenital deafness is often the result of the improper development or degeneration of cochlear hair cells which form the tiny hairs in the ear that detect sound.

In one type of Usher syndrome – known as Type 1 Usher Syndrome – which French settlers brought to the USA hundreds of years ago, there is a problem with a protein called harmonin. Harmonin is required in order to form the cochlear hair cells. The same problem also causes gradual loss of vision.

In type 1 Usher syndrome, there is a mutation in the USH1C gene. This gene controls the production of harmonin. When USH1C has a fault (mutation), it produces truncated forms of harmonin.

Michelle Hastings, at the Rosalind Franklin University of Medicine and Science in Chicago, Illinois, and team designed a genetic patch – a tiny strip of genetic material – which becomes attached to the mutated gene, corrects it, and results in proper building of harmonin.

They injected the mice, which had been genetically engineered to have Usher syndrome, with the genetic patch. Initially, they all grew up with no balance problems and reasonable hearing. This went on for a couple of months; their hearing was near-normal in the lower frequencies.

After the experiment, the researchers dissected the mice and found that some hair cells had grown in their cochleae.

However, within six months, their hearing started to deteriorate.

In an Abstract in Nature Medicine, the authors wrote:

“These effects were sustained for several months, providing evidence that congenital deafness can be effectively overcome by treatment early in development to correct gene expression and demonstrating the therapeutic potential of ASOs (antisense oligonucleotides) in the treatment of deafness.”

In an interview with the BBC, Professor Hastings said they were surprised that mice could be treated immediately after birth with “such a profound effect”. In order to get good results, the mice need to be treated within the first ten to thirteen days of life.

The scientists are not sure whether treatment is only effective if performed soon after birth because timing is crucial for efficacy, or whether the patch is simply not able to get to the target area beyond a certain point.

Human fetuses spend 9 months in their mother’s uterus, compared to just three weeks in the case of mice. If the key is timing, this could raise problems in developing a similar treatment in humans. The authors said that perhaps treatment might have to be carried out while the human baby (fetus) is still in the womb.

Scientists from Massachusetts Eye and Ear Harvard Medical School reported in the journal Neuron (January 2013 issue) that they managed to get the tiny hairs in the cochlea of mice to regrow by using a drug, thus restoring partial hearing.

Researchers from the University of Sheffield, England, managed to reverse a form of deafness in gerbils using human embryonic stem cells – they repaired the auditory nerve. They reported their work in Nature (September 2012 issue). The gerbils had a similar from of hearing loss due to auditory neuropathy, which affects humans – the cochlear nerve (auditory nerve) is damaged.

Written by Christian Nordqvist