Genetic Causes of Hearing Loss

Genetics play a huge role in hearing loss and deafness in both infants and the elderly. About 60 to 80 percent of deafness in infants (congenital deafness) can be attributed to some kind of genetic condition.

It is also possible to have a mix of genetic hearing loss and acquired hearing loss. Acquired hearing loss is hearing loss that occurs because of an environmental cause such as medication side effects or exposure to chemicals or loud noises.

Genetic Syndromes That Cause Hearing Loss

Not all congenital hearing loss is genetic, and not all genetically related hearing loss is present at birth. While the majority of hereditary hearing loss is not associated with a specific syndrome, many genetic syndromes (possibly more than 300) are associated with congenital hearing loss, including:

• Alport Syndrome: characterized by renal failure and progressive sensorineural hearing loss.
• Branchio-Oto-Renal syndrome
• X-linked Charcot Marie Tooth (CMT): also causes peripheral neuropathy, problems in the feet, and a condition called "champaign bottle calves."
• Goldenhar’s Syndrome: characterized by the underdevelopment of the ear, nose, soft palate, and mandible. This may affect only one side of the face, and the ear may appear partially formed.
• Jervell and Lange-Nielsen Syndrome: in addition to sensorineural hearing loss, this condition also causes cardiac arrhythmias and fainting.
• Mohr-Tranebjaerg Syndrome (DFN-1): this syndrome causes sensorineural hearing loss that begins in childhood (usually after a child has learned how to speak) and gets progressively worse. It also causes movement problems (involuntary muscle contractions) and difficulty swallowing among other symptoms.
• Norrie Disease: this syndrome also causes problems with eyesight and mental disturbances.
• Pendred Syndrome: Pended syndrome causes sensorineural hearing loss in both ears along with thyroid problems (goiter).
• Stickler Syndrome: stickler syndrome has many other characteristics in addition to hearing loss. These may include cleft lip and palate, eye problems (even blindness), joint pain or other joint issues, and specific facial characteristics.
• Treacher Collins Syndrome: this syndrome results in an underdevelopment of the bones in the face. Individuals may have abnormal facial characteristics, including eyelids that tend to slant downward and little to no eyelashes.
• Waardenburg Syndrome: in addition to hearing loss this syndrome can cause eye problems and abnormalities in the pigment (color) of the hair and eyes.
• Usher Syndrome: can cause both hearing loss and vestibular problems (dizziness and loss of balance).

Non-Syndromic Causes of Genetic Hearing Loss

When hereditary hearing loss is not accompanied by other specific health problems it is called non-syndromic. The majority of genetic hearing loss falls into this category.

Non-syndromic hearing loss is usually caused by genes that are recessive. This means that if one parent passes the gene associated with hearing loss, it will not be expressed or won't occur in the child. Both parents need to pass a recessive gene to the child in order for the hearing loss to be present.

While hearing loss related to a recessive gene would seem unlikely to occur, about 70 out of 100 cases of hearing loss are non-syndromic and 80 out of 100 of those individuals have hearing loss that was caused by recessive genes. The remaining 20 percent occurs as a result of dominant genes, which only requires the gene from one parent.

How Do My Care Providers Label My Genetic Cause of Hearing Loss?

If you are reviewing your healthcare provider's notes, you may find acronyms that you do not understand. Here is an explanation of how non-syndromic hearing loss may be labeled in healthcare provider notes:

1. named by the disorder
   ___-related deafness (where ___ is the gene causing deafness)
2. named by gene location
   DFN simply means deafness
3. A means autosomal dominant
4. B means autosomal recessive
5. X means X-linked (handed down through the parents X chromosome)
6. a number represents the order of the gene when mapped or discovered

For example, if the hearing disorder is named by the specific gene by your practitioner, you may see something similar to OTOF-related deafness. This would mean that the gene OTOF was the cause of your hearing disorder. However, if your healthcare provider used the gene location to describe the hearing disorder, you would see a combination of the points listed above, like DFNA3. This would mean that the deafness was an autosomal dominant gene with a 3rd order of gene mapping. DFNA3 is also referred to as connexin 26-related deafness.

How Can a Genetic Hearing Loss Disorder Be Identified?

Identifying genetic causes, also referred to by healthcare providers as etiology, can be very frustrating. To help minimize the difficulty in identifying the cause, you should have a team-based approach. Your team should consist of an otolaryngologist, audiologist, geneticist, and a genetics counselor. This seems like a big team, however with more than 65 genetic variants that can cause hearing loss, you will want to minimize the amount of testing if any is needed.

Your otolaryngologist, or ENT, may be the first healthcare provider you see in trying to determine the cause of genetic hearing loss. They will do a detailed history, complete a physical exam, and if necessary refer you to an audiologist for a thorough audiology workup.

Other lab work may include toxoplasmosis and cytomegalovirus, as these are common prenatal infections that can cause hearing loss in infants. At this point, common syndromic causes of hearing loss may be identified and you can be referred to a geneticist to test for the specific genes associated with the suspected syndrome.

Once common syndromes have either been identified or eliminated, your ENT will recommend you to a geneticist and genetic counselor. If there are suspected genetic variants that are suspected, testing will be limited to those genes. If there is not a suspected genetic variant, then your geneticist will discuss what testing options are best to be considered.

Your geneticist will take the information from the audiology evaluation to help rule out some of the testing. They may also order other tests like an electrocardiogram (ECG or EKG) to look at your heart rhythm, which will also help narrow down what they test for. The goal is for the geneticist to maximize the benefit of the testing before ordering tests that could be a waste of time, effort, and resources.