A short strip of genetic material has been used to prevent hereditary deafness in mice. In a mouse model of the human condition Usher syndrome, which affects hearing, vision and balance, a 'genetic patch' was able to bind to and correct the mutation responsible for the condition. This ensured the proper assembly of a protein vital for the ability to hear and maintain balance.
Dr Michelle Hastings, who led the study at Rosalind Franklin University of Medicine and Science, Chicago, USA said: 'A single dose of the drug ['genetic patch'] to newborn mice corrects balance problems and allows these otherwise deaf mice to hear at levels similar to non-Usher mice for a large portion of their life'.
Approximately one in 6,500 children in the UK are born with Usher syndrome, resulting in varying degrees of deafness and blindness. Type 1 Usher syndrome is due to a mutation in the gene, USH1C, which codes for the protein harmonin. The mutation causes the protein to be produced in a stunted form that is not fully functional. Harmonin is important for the development of sensory hair cells in the inner ear, which send electrical signals to the brain when they detect sound.
Researchers injected newborn Usher mice with a genetic sequence, called an antisense oligonucleotide (ASO), which specifically targeted the mutation in the USH1C gene. This partially restored normal harmonin production.
The treated Usher mice showed normal growth of sensory hair cells needed to detect low-range sound frequencies; this was less apparent for hair cells needed to detect higher frequencies. Measuring nerve responses to sound showed Usher mice who received the therapy were able to detect low frequency sounds to a similar extent as normal mice. These therapeutic effects lasted several months, but by six months the hearing ability of the treated mice began to diminish.
Dr Hastings' team found that timing was crucial – the mice needed to be treated within the first 10-13 days after birth in order for the treatment to show a significant effect. This suggests that in humans, who have a far longer gestation period, the therapy would need to be given whilst the baby is still in the womb and would therefore require a complex delivery system, reports the BBC.
Previously, stem cells have been used to try to cure deafness in mice (as reported in BioNews 558) by generating new inner ear hair cells. The current study, published in Nature Medicine, demonstrates that congenital deafness in mice can be temporarily overcome using gene therapy.
Dr Ralph Holme, head of biomedical research at Action on Hearing Loss, said: 'More research is now needed to understand how this new therapy could be used to treat this particular type of Usher Syndrome in humans and discover whether vision can also be rescued'.