Genetics and Cochlear Implants
Genetics and hearing loss in children
In developed countries sensorineural hearing loss occurs in approximately 1 of every 500 new-born children.
The causes could come from the environment. For example the new born could have contracted cytomegalovirus from a maternal infection or was exposed to ear damaging antibiotics in utero. In approximately 70% of new born children it is thought that damage to hearing comes from the environment.
In the remaining children it is thought that genetics play an important role
Some genetic causes are easy to identify. For example Pendred Syndrome, Usher syndrome etc.
Most congenital Sensorineural hearing loss is autosomal recessive also known as ARSNHL. It is been found that mutations in one gene can account for 50% of congenital ARSNHL.
It has been found that a small population of children ( around 3% to 7%) do not benefit from cochlear implants.
If the gene mutation is found in the membranous labyrinth then the child is likely to experience benefit from the cochlear implant. This is because it is not the end organ being stimulated by the cochlear implant.
It holds true that should the genetic mutation be in the spiral ganglion cells which is the end organ being stimulated by the cochlear implant, then, that child is unlikely to experience any significant benefit from the cochlear implant.
It is thus logical to think that genetic testing should be mandatory in helping discern which child will benefit from cochlear implants and who will not. Unfortunately at this time such extensive testing is not available.
The genes linked to deafness in children currently under investigation are GjB2, SLC26A4, OTOF (otoferlin) mutations. These are membranous expressed genes. The Spiral ganglion expressed genes are TMPRSS3, CHD7 and DDP1 / TIMM8a.
There have been a few reports on mitochondrial deafness. In the cochlea the cells that demand the highest amount of energy are the hair cells and the stria vascularis. As a result, mitochondrial deafness would likely affect these high energy areas like the stria vascularis and the hair cells. Patients suffering from deafness caused by mitochondria would likely benefit from cochlear implants.
In conclusion it can be said that advanced genomic and sequencing technology will help us understand where the problem is located and thus help us discern which new-born will benefit from a cochlear implant and who will not.
This in turn will allow for care based on the child’s unique genetic traits.