Genetic deafness

14 03 2010

At my annual ENT consultation, we discussed the possible cause of my hearing loss.  I was born 3 months premature and stayed in an incubator for 3 months, so the cause of my deafness may have been environmental, from the noise of the incubator’s motor.  As part of the cochlear implant assessment process, I had a CT scan and MRI scan, which showed no skull or ear abnormalities. The consultant said the cause of my deafness is therefore at a microscopic level, and decided to carry out genetic testing as a permanent hearing loss is genetic in 50% of cases.

There is no one else in my family with deafness (apart from age-related). I may have inherited one faulty gene from my mother or one from my father (dominant inheritance), or the same faulty gene from both parents (recessive inheritance). My parents may be carriers, having the altered gene but not the characteristic of it. Occasionally, a gene mutation can be a one-off.  Not all hearing loss genes have been identified.

(Graph source: Centre for Genetics Education)

In 50% of deaf persons, the cause of deafness is a combination of genetic and environmental influences such as noise, age, ototoxic drugs, head injuries or infection.

In the other 50%, genetics alone is the cause.  If other symptoms present themselves in conjunction with a genetic hearing loss, these can point to a syndrome (such as retinitus pigmentosa for Ushers) in 30% of these cases. The other 70% of this group are non-syndromic cases, i.e. deafness occurs by itself; over 100 genes have been identified to cause this type of deafness.

Within the pre-lingual non-syndromic hearing loss group that is genetic, 75%-80% of cases follow a pattern of autosomal recessive inheritance in families. Where both parents are unaffected carriers of the faulty gene involved, there is a 25% chance in every pregnancy that their child will be affected. The most common gene involved in this group is called Connexin 26 but there are many others. An altered Connexin 26 gene affects the functioning of the cochlear hair cells, causing a sensori-neural hearing loss, where the sound cannot be transmitted to the auditory nerve and onwards to the brain. I had a blood sample taken to be tested for Connexin 26 and await the lab results.

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2 responses

15 03 2010
Lissa

I like you was born 3 months prematuely and stayed in hospital for 3 months, they think medication is the cause of my deafness since I do not have connexion 26 or the other things they tested for

15 03 2010
Speakuplibrarian

Very interesting. I am the only one in my family (on both sides) who has a hearing loss with one exception. When my grandfather was in his eighties he was given an ototoxic medicine in the hospital which took away his hearing. No one else has a sensorineural hearing loss like myself. Since I don’t know the cause of my hearing loss, I tend to wonder if my son will have hearing loss in his future. Is it expensive to be tested for connexion 26?

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