A potential cure for hereditary deafness has been discovered by scientists who used only one dose of CRISPR-Cas9 to successfully treat mice with a progressive hearing loss.

CRISPR-Cas9 is described to be the most simple, accurate, and affordable method in editing animal genes. It is yet to be tested on humans but many are proposing that after years of research and development, it could possibly cure genetic diseases and even aid in human reproduction.

The recent experiment conducted by a research team from Howard Hughes Medical Institute is among the first to use gene engineering to treat deaf animals.

Tmc1 Mutation Causes Progressive Hearing Loss

The mice included in the experimental group suffered from a rare form of progressive hearing loss caused by a mutation in the Tmc1 or Beethoven gene. It targets the hair cells located in the inner ear, which is responsible for detecting sound waves and transmitting them to the brain.

A new report explains that the mutation instructs the hair cells to produce a poisonous protein causing their gradual death. As more of these cells die in the inner ear, the more advanced hearing loss becomes until it ultimately ends up in irreversible deafness.

Moreover, the Tmc1 mutation is classified as dominant. This means that even just a single copy of the mutated gene can already result in a progressive hearing loss. Dominant mutations could not be corrected by traditional forms of therapy but through CRISPR-Cas9, the team removed the Tmc1 gene stopping production of the poisonous protein.

CRISPR-Cas9 Removes Beethoven Mutation To Cure Hearing Loss In Mice

The Wellcome Genome Campus describes the enzyme Cas9 to work like a pair of scissors. To disable a gene, it simply snips two strands of DNA in a targeted area. However, this method was not applicable to the experiment as using Cas9 alone runs the risk of cutting other genes with a similar appearance as the mutated Tmc1 gene.

To avoid such, the team packaged Cas9 with a guide RNA. Such bundle was designed to slip into cells to cut the mutated gene and then quickly disintegrate before causing damage to non-target genes. Each mouse was injected with a single dose.

After eight weeks, the team reports in a study published Dec. 20 that the experimental group had regrown healthy hair cells in their inner ear. Also, monitoring the mice's brain signals proved that they were capable of hearing sounds that are 15 decibels softer than their untreated counterparts. This led to the conclusion that CRISPR-Cas9 is "a potential strategy" for hearing impairment caused by genetic mutations.

"We hope that the work will one day inform the development of a cure for certain forms of genetic deafness in people," says HHMI chemical biologist David Liu.

More research is needed before the team's CRISPR-Cas9 can be used on hearing-impaired humans. According to Liu, their genetic engineering technique would be most effective in children with Tmc1 mutation whose hearing loss is still in early stages.

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