Hearing loss in later life and early deafness are caused by mutation in hearing-related gene. Scientists at the Scripps Research Institute (TSRI) recently determined that a single gene is responsible for our hearing. They’ve also discovered the exact cause of deafness while suggesting new avenues for hearing therapies.
The TSRI study, published in the journal Neuron, reveals how mutations in a gene called Tmie can cause deafness right from birth or hearing decline in later years.
Researchers were able to examine the hair cells of so-called knock-out mice, using electrophysiological techniques over six months. They then reintroduced the Tmie gene in the population before bringing back the very process that reinforces hearing. That means that one day, we might be able to use gene therapy approaches to hearing loss.
Of course, scientists have long known that mutations in the Tmie gene could cause deafness, yet they’ve never been sure how that could be.
Without question, the ear is complicated machinery. It basically changes mechanical sound waves into electric signals in order for our brains to process the message.
When a sound wave enters our ear, the uneven ends – stereocilia – of the inner ear’s hair cells are pushed back. Think of them as tiny blades of grass that are constantly bent by the wind. This kind of movement creates tension in the strings of proteins that connect the stereocilia. This then sends a signal to our brain.
Nevertheless, this process of converting mechanical force into electrical activity – what’s called mechanotransduction – is a mystery to researchers.
Did you know that one of the most common birth defects is hearing loss or congenital deafness? It’s true.
In fact, it affects about three out of 1,000 infants born. Genetic defects play a key role in congenital hearing loss, and this contributes to roughly 60 percent of deafness that happens in babies. Of course, genetic defects aren’t the only factor leading to hearing loss and deafness. Others may include trauma, environmental exposure, medical problems, and medications.
So how do genes work exactly? Well, essentially, they’re a road map for the synthesis of proteins, which are the building blocks for everything in our bodies, like hair, eyes, heart, lungs – and ears.
Each of us inherits half of all genes from one parent and half from the other. If some of these inherited genes are defective, a health disorder like hearing loss or deafness can develop early or later in life, according to the American Academy of Otolaryngology.
In the past 10 years, advances in molecular biology and genetics have helped us to better understand the development, function, and pathology of the inner ear. Researchers have pinpointed various genes that are behind hereditary deafness and hearing loss – most notably, the GJB2 gene mutation.
As a result, screening tests for the GJB2 gene are available to people so that they can determine their risk of having a child with hearing problems.
Now that researchers have learned how mutations in the gene Tmie can cause hearing difficulties, the challenge will be to find out how the many components of the mechanotransduction system take shape in the inner ear’s hair cells. In the future, we’ll also need to understand the biophysical principles through which these same proteins turn mechanical signals into electrical ones in the first place.
It’ll only give more hope to those who are hard of hearing.