Hearing loss has been one of those invisible and mostly insoluble afflictions that cause stress and suffering for many. However, now scientists are drawing closer to finding the cause of many congenital forms of deafness and in the process are uncovering possible solutions and cures.
The last two years in particular have witnessed some very exciting new developments in the world of gene research. And the good news for the hard of hearing is that there may be light (and sound) at the end of the long dark tunnel.
Identifying the proteins that trigger hearing loss
In 2014, a team of researchers in France discovered that the absence of a particular protein or a malfunction in the gene that generates that protein causes profound deafness in mice and humans.
Three variants of this protein, protocadherin-15, exist in the inner ear and play a key role in transforming sound into electrical signals that can be processed by the brain. Christine Petit, Ph.D., and her team at the Institut Pasteur in Paris and at Collège de France engineered mice that were missing the CD2 isoform of this protein and observed that the mice became completely deaf.
The absence of the other two variants of the protein had no discernible effect on the mice’s hearing. The same genetic mutation was observable in profoundly deaf children allowing researchers to extrapolate these results to humans.
This discovery opens up the field for further research into gene therapy that will reverse this particular form of hereditary hearing loss.
Also in 2014, a joint study conducted by the National Institutes of Health’s National Institute on Deafness and Other Communication Disorders (NIDCD) and the National Heart, Lung, and Blood Institute (NHLBI) made great progress in exploring the function of the myosin 15 protein. Myosin 15 is thought to be pivotal in the development of healthy hearing structures such as stereocilia.
Likewise, problems with this protein are a major cause of hereditary hearing loss and an increased understanding of the function of myosin 15 will play a key role in developing effective gene therapies.
It’s all in the genes
With mutations in more than 70 different genes being responsible for hereditary deafness in humans there remains a lot of work to isolate, map and understand this area of hearing loss. But each step taken is a step closer to a cure.
In July this year, scientists at École Polytechnique Fédérale de Lausanne made an extraordinary breakthrough in gene therapy with the gene, TMC1, a gene that when it mutates causes around 4-8% of genetic deafness in humans.
Children with a recessive or mutant form of TMC1 usually develop profound deafness by the age of two to fifteen years old. Currently, the only solutions in such cases are hearing aids or cochlear implants.
The scientists worked with mice that had been engineered with two mutant forms of the TMC1 gene to mimic the deafness found in similarly affected humans.
Scientists injected the deaf mice with an engineered virus and a promoter to carry a healthy version of the TMC1 gene. The results were exciting: a measurable electrical pulse in the hair cells and restoration of hearing. The engineered virus carrier is already in use in other human trials but there is still some work to do before this gene therapy is ready for human trials–possibly within 5-10 years time.
Again, it’s those genes
Other exciting developments this year have mirrored this success. Scientists at the University of California, San Francisco had similar success with a different gene. The protein, vesicular glutamate transporter-3 (VGLUT3), formed by this particular gene is vital for processing sound into electronic signals. Likewise, this gene, in a mutant form, causes hereditary deafness in humans.
Again, using engineered mice, the researchers were able to reverse the induced hearing loss by injected healthy forms of the genetic material.
Lawrence Lustig, one of the leaders of this study says, “For years, scientists have been hinting at the possibility of gene therapy as a potential cure for deafness. In this study, we now provide a very real and big step towards that goal.”
Science may soon have the answer
Current estimates suggest that the human body contains some 2 million proteins, which are formed from between 25,000 to 30,000 genes. Unfortunately, it may only take a slight malfunction in a tiny isolated piece of the genetic code to cause havoc in the human body. But the good news is that as scientists rapidly narrow their focus down to the culprit genes they are making great strides in the search for a cure for deafness.
Keep up with the latest developments at https://www.houseofhearing.ca/.