Mitochondrial Disorders and Hearing Loss

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Mitochondria are tiny “power plants” that produce a body’s essential energy.

As many as 2 million Americans suffer from mitochondrial disease. Doctors and researchers have identified hundreds of different subtypes of the disorder. Mitochondrial disease or dysfunction is an energy production problem. Almost all cells in the body have mitochondria, which are tiny “power plants” that produce a body’s essential energy.

Mitochondrial disease means the power plants in cells don’t function properly.

When that happens, some functions in the body don’t work normally. It’s as if the body has a power failure: there is a gradation of effects, like a ‘brown out’ or a ‘black out.’

Scientifically, it is actually a category or group of diseases. That’s why mitochondrial disease takes many different forms and no two people’s symptoms may look alike.

Hearing loss is a common finding in mitochondrial disease but may be undetected for years or pushed to the side while more acute or physically disabling symptoms are treated first. Typically, hearing loss will affect the high frequencies first and spread to the mid and low frequencies. Both ears are generally affected symmetrically. Treatment for hearing loss involves the use of hearing aids, assistive listening devices, and/or cochlear implants.

Hearing aids are useful when the hearing loss is peripheral. This means that the hearing loss is affecting the cochlea or auditory nerve dysfunction.

Most cases of hearing loss associated with mitochondrial disorders fall into this category. The effect of hearing loss on communication and development is well documented, and hearing should be tested regularly in people with mitochondrial disorders in order to identify and treat the hearing loss as early as possible.

Digital hearing aids have a lot of flexibility and can accommodate changes in hearing loss; the audiologist can program the hearing aids an unlimited number of times to ensure the person has the most access to sound possible.

In the event that hearing loss progresses past the point where hearing aids are able to compensate for the loss, cochlear implantation is a possibility. A physician specializing in mitochondrial disorders is an essential member of the cochlear implant team and should be involved before, during, and after the surgery to obtain the best outcomes.

The other type of hearing loss that can occur in mitochondrial disease is central hearing loss. This is hearing loss due to involvement of the brainstem, midbrain, or higher level in the auditory cortex. Central hearing loss does not respond to hearing aids, and intervention should be targeted to more visual forms of communication. Patients with central hearing loss typically have inconsistent auditory behavior that may cause them to be misdiagnosed initially.

Central involved "deaf" patients may have reactions to environmental sounds, despite absence of reaction to loud noises.

Avoiding aminoglycosides and noise exposure, especially in those with normal hearing who have the m.1555A>G pathogenic variant in MT-RNR1, can be an important step in preventing hearing loss. In the United States, aminoglycoside use is most common in the neonatal intensive care unit. In a family with this known variant, prospective molecular genetic testing of at-risk maternal relatives allows early detection of those who have inherited the pathogenic variant and would benefit from avoiding aminoglycosides to prevent onset of hearing loss.

Sources

Overview of Mitochondrial Disease (nd). Foundation for Mitochondrial Medicine. Accessed 1/27/2015 from http://mitochondrialdiseases.org/mitochondrial-disease/ 

Chinnery, Patrick. Audiology – The United Mitochondrial Disease Foundation. Accessed 1/27/2015 from http://www.umdf.org/atf/cf/%7B858ACD34-ECC3-472A-8794-39B92E103561%7D/Audiology.pdf 

Hain TC, Micco A. Cranial Nerve 8: Vestibulocochlear Nerve. Textbook of Neurology, Goetz and Pappert Ed, Saunders, 2003, (2nd Edn) 

Pandya, Arti (October 2004). Nonsyndromic Hearing Loss and Deafness, Mitochondrial. GeneReviews. Accessed 1/27/2015 from http://www.ncbi.nlm.nih.gov/books/NBK1422/ 

About Mitochondrial Disease - Mito FAQ (n.d.). MitoAction. Accessed 1/27/2015 from http://www.mitoaction.org/mito-faq 

Mitochondrial Disease (n.d.). Cleveland Clinic. Accessed 1/27/2015 from http://my.clevelandclinic.org/services/neurological_institute/pediatric-neuroscience/pediatric-neurology/diseases-conditions/mitochondrial-disease.

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