Lecture By Dr Mark Downs on causes and treatment of hearing loss

Hearing – the difference.

On Wednesday, March 23^rd, following our AGM, the Society’s  Chief Executive, Dr Mark Downs, gave us a most interesting and informative lecture on Hearing Loss.

At first Mark talked about the stigma and social isolation that deafness may bring and the way we feel that it is acceptable to laugh at deafness, but not at other disabilities, illustrating splendidly by a video of Rowan Atkinson being fitted with a comic apparatus to inform him when the telephone rang. Of course he was unable to hear anyone on the ‘phone when he did answer it. Mark then pointed out that some 14% of the population have hearing problems including more than 20,000 children, resulting in some two million people in this country having hearing aids. Possibly as a result of the associated isolation a higher proportion of deaf people have mental health problems than do the hearing members of the population.

Mark then went on to describe in some detail the anatomy and functioning of the ear including the roles of the 15,500 or so hair cells within the cochlea; contrasting this number with the mere 16 receptors in the most advanced cochlea implant. A comparison made more stark by a recording of the poor quality sound received by a patient with an implant listening to human speech.

Hair cells from Guinea pig cochlea

Mark then went on to discuss the biochemical mechanism by which sound generates an action potential in the auditory nerve. In outline this involves vibrations in the inner hair cells opening ion channels to permit the influx of potassium ions. This ingress then depolarised the membrane and permits the influx of calcium ions which stimulate the release of glutamate, a neurotransmitter; a delicate mechanism easily disrupted e.g. by aminoglycosidic antibiotics, by platinum derivatives given as treatment for some cancers or, more commonly, by excessive noise over a prolonged period. For example 90 decibels, easily generated by an MP3 player, can cause hearing damage after regular use even for periods of less than one hour.

Hearing loss has also been associated with smoking, with obesity, and with mutations in over 100 different genes. For example mutations in the GJB2 gene, which codes for a protein Connexin 26 (CX26), have been associated with some 50% of all childhood deafness.

Another common cause of deafness is Ushers syndrome, an autosomal recessive trait, responsible for deafness in four babies in every 100,000 births and in the most severe cases, for deaf blindness from birth.

Mark then went on to talk about tinnitus, the debilitating effect that it can have on sufferers, and the relative absence of effective treatments.

Then finally we heard about current and possible treatments for deafness including hearing aids, cochlear implants, brain cell implants and, more speculative, drug treatments or gene therapies to prevent damage and the possible use of stem cells to reverse damage, a process as yet impossible in humans but commonplace in reptiles.

The lecture was followed by a large number of interesting and relevant questions and an appreciative round of applause.