Is there cause for optimism when it comes to preventing hearing loss? Certainly the latest research into this suggests that if positive effects experienced by mice could be transferred to humans and maintained for the long term, then hereditary hearing loss could be a thing of the past.
It has always been assumed that hearing loss is always down to old age. The commonly held view is that as people grow older, their muscles and body functions deteriorate with time to the point that muscle function is impaired and eventually lost. But hearing loss is not necessarily down to age, although there are cases where constant exposure to loud noise, over time, causes reduced sensitivity to aural stimuli. Over half of hearing loss cases are actually due to inheriting faulty genetic mutations from parents.
How do we hear? The hair cells of the inner ear called the cochlea respond to vibrations and these signals are sent to the brain to interpret. The brain processes these signals in terms of frequency, duration and timbre in order to translate them into signals we know.
For example, if we hear a high frequency sound of short duration that is shrill, our brain interprets these characteristics and then runs through a database of audio sounds, an audio library in the brain, and may come up with the suggestion that it has come from a whistle and may signify a call for attention.
What happens when you have a genetic hearing loss gene? The hairs on the inner ear do not grow back and consequently sound vibration from external stimuli do not get passed on to the brain.
With progressive hearing loss too, the characteristics of sound also get distorted. We may hear sounds differently to how they are produced, thereby misinterpreting their meaning. Sounds of higher and lower frequency may be less audible too.
How does that cause a problem? Imagine an alarm. It is set on a high frequency so that it attracts attention. If your ability to hear high frequencies is gradually dulled then you may not be able to detect the sound of an alarm going off.
As hearing gradually deteriorates, the timbre of a sound changes. Sharper sounds become duller, and in the case of the alarm, you may hear it, but it may sound more muted and the brain may not be able to recognise that it is an alarm being heard.
Another problem with hearing loss is the loss of perception of volume. You may be crossing the road and a car might sound its horn if you suddenly encroach into its path. But if you cannot hear that the volume is loud, you may perceive it to be from a car far away and may not realise you are in danger.
The loss of the hairs in the inner ear is a cause of deafness in humans, particularly those for whom hearing loss is genetic. Humans suffering from hereditary hearing loss lose the hairs of the inner ear, which result in the difficulties mentioned above. But there is hope. In a research experiment, scientists successfully delayed the loss of the hairs in the inner ear for mice using a technique that edited away the genetic mutation that causes the loss of the hairs in the cochlea.
Mice were bred with the faulty gene that caused hearing loss. But using a technology known as Crispr, the faulty gene was replaced with a healthy normal one. After about eight weeks, the hairs in the inner ears of mice with genetic predisposition to hearing loss flourished, compared to similar mice which had not been treated. The genetic editing technique had removed the faulty gene which caused hearing loss. The treated mice were assessed for responsiveness to stimuli and showed positive gains.
We could be optimistic about the results but it is important to stress the need to be cautious.
Firstly, the research was conducted on mice and not humans. It is important to state that certain experiments that have been successful in animals have not necessarily had similar success when tried on humans.
Secondly, while the benefits in mice were seen in eight weeks, it may take longer in humans, if at all successful.
Thirdly, we should remember that the experiment worked for the mice which had the genetic mutation that would eventually cause deafness. In other words, they had their hearing at birth but were susceptible to losing it. The technique prevented degeneration in hearing in mice but would not help mice that were deaf at birth from gaining hearing they never had.
Every research carries ethical issues and this one was no different. Firstly, one ethical issue is the recurring one of whether animals should ever be used for research. Should mice be bred for the purposes of research? Are all the mice used? Are they accounted for? Is there someone from Health and Safety going around with a clipboard accounting for the mice? And what happens to the mice when the research has ceased? Are they put down, or released into the ecosystem? “Don’t be silly,” I hear you say, “it’s only mice.” That’s the problem. The devaluation of life, despite the fact that it belongs to another, is what eventually leads to a disregard for other life and human life in general. Would research scientists, in the quest for answers, eventually take to conducting research on beggars, those who sleep rough, or criminals? Would they experiment on orphans or unwanted babies?
The second, when it comes to genetics, is whether genetic experimentation furthers good or promotes misuse. The answer, I suppose, is that the knowledge empowers, but one cannot govern its control. The knowledge that genetic mutation can be edited is good news, perhaps, because it means we can genetically alter, perhaps, disabilities or life-threatening diseases from the onset by removing them. But this, on the other hand, may promote the rise of designer babies, where mothers genetically select features such as blue eyes for their unborn child to enhance their features from birth, and this would promote misuse in the medical community.
Would the use of what is probably best termed genetic surgery be more prominent in the future? One can only suppose so. Once procedures have become more widespread it is certain to conclude that more of such surgeons will become available, to cater for the rich and famous. It may be possible to delay the aging process by genetic surgery, perhaps by removing the gene that causes skin to age, instead of using botox and other external surgical procedures.
Would such genetic surgery ever be available on the NHS? For example, if the cancer gene were identified and could be genetically snipped off, would patients request this instead of medical tablets and other external surgical processes? One way of looking at it is that the NHS is so cash-strapped that under QALY rules, where the cost of a procedure is weighed against the number of quality life years it adds, the cost of genetic surgery would only be limited to more serious illnesses, and certainly not for those down the rung. But perhaps for younger individuals suffering from serious illnesses, such as depression, the cost of a surgical procedure may far outweigh a lifetime’s cost of medication of anti-depressant, anti-psychotics or antibiotics. If you could pinpoint a gene that causes a specific pain response, you might alter it to the point you may not need aspirin, too much of which causes bleeds. And if you could genetically locate what causes dementia in another person, would you not be considered unethical if you let the gene remain, thereby denying others the chance to live a quality life in their latter years?
Genetic editing may be a new technique for the moment but if there is sufficient investment into infrastructure and the corpus of genetic surgery information widens, don’t be surprised if we start seeing more of that in the next century. The cost of genetic editing may outweigh the cost of lifelong medication and side effects, and may prove to be not just more sustainable for the environment but more agreeable to the limited NHS budget.
Most of us won’t be around by then, of course. That is unless we’ve managed to remove the sickness and death genes.