Harvard Medical School and Boston Children's Hospital scientists, using a novel gene editing approach, were able to save the hearing of mice that suffered from genetic hearing loss.
Known as Beethoven mice, scientists treated them for the same genetic mutation that causes progressive hearing loss in people, with most suffering from complete deafness by the time they reach their mid-20s. Scientists used a refined version of the CRISPR-Cas9 gene-editing system to selectively disable the defective copy of the hearing gene dubbed Tmc1 and leave the healthy copy intact.
The mice that have the faulty Tmc1 gene are known as Beethoven mice because their disease is the same hearing loss that the famed composer suffered from.
Every human inherits two copies of the same gene from each parent. Most of the time one normal gene is enough to prevent an individual from diseases but with inherited genetic disorders one bad copy of the gene can cause the disease.
Research Paves the Way for More Hyper Targeted Gene-Editing Therapy
According to the research, scientists were able to pinpoint a single incorrect DNA letter in the defective copy which was among 3 billion letters in the genome of the mouse. The researchers cautioned a lot more work needs to be done before it could be used in humans but is still considered a milestone. With the achieement, a similar approach can be used to treat other genetic diseases that are caused by a single defective copy of a gene.
"Our results demonstrate that this more refined, better-targeted version of the now-classic CRISPR/Cas9 editing tool achieves an unprecedented level of identification and accuracy," said study co-senior investigator David Corey, the Bertarelli Professor of Translational Medical Science in the Blavatnik Institute at Harvard Medical School. The researcher went on to say that their work paves the way for a hyper-targeted way to treat a slew of genetic disorders that are caused by a defective copy of a gene.
Much More Work Need to be Done
To test the effectiveness of the therapy, the researchers measured the mice' auditory brainstem responses, capturing how much sound is detected in the hair cells in the inner ear and sent to the brain. Without the treatment, the Beethoven mice were completely deaf by six months. Mice without the genetic defect maintained normal hearing throughout their life and can hear sounds around 30 decibels. The Beethoven mouse was cable of hearing sounds at similar decibels two months after the gene editing therapy.
"To be sure, this is the first step in a long journey," study co-senior investigator Jeffrey Holt, Harvard Medical School professor of otolaryngology and neurology at Boston Children's Hospital, who is also affiliated with the F.M. Kirby Neurobiology Center at Boston Children's. "But what we have here is proof of principle that demonstrates this highly specific, highly targeted treatment could be developed to selectively silence genes that carry single-point mutations and potentially treat many other forms of human disease."