What is Genetic Hearing Loss?
Hearing loss affects your ability to hear and can significantly impact your social interactions and language development over time. It can occur either before you’ve learned to speak or after. There are several types of hearing loss, including conductive hearing loss, where the transmission of sound from your outer or middle ear to your inner ear is reduced. Another type is sensorineural hearing loss, caused by problems with your inner ear or the nerve that connects your ear to your brain.
Some people may experience both types of hearing loss, which is known as mixed hearing loss. Sensorineural hearing loss can be due to factors like exposure to loud noise (acquired) or can be inherited (genetic). This discussion is about genetic sensorineural hearing loss, its visibility in your family line, how it’s diagnosed, and how it’s managed.
What Causes Genetic Hearing Loss?
About half the people with hearing loss have it because of their genes. The other half lose their hearing for other reasons such as infections, injuries, exposure to loud noise, or harmful side effects from drugs, called ototoxicity.
There are two types of genetic hearing loss: syndromic and non-syndromic. ‘Syndromic’ means the hearing loss is part of a wider medical condition or syndrome, and it makes up about 30% of inherited hearing loss. ‘Non-syndromic’ on the other hand, means the hearing loss is the only symptom, and it covers the remaining 70% of genetic hearing loss cases.
Within the non-syndromic category, the most common type of inheritance pattern is autosomal recessive — this means both parents carry a copy of the gene mutation and the chance of a child having hearing loss is 1 in 4, or 25%. This pattern accounts for around 75-80% of non-syndromic hearing loss cases.
Autosomal dominant hearing loss, where only one parent carries the gene mutation and there is a 50% chance of passing it to their child, accounts for about 20% of non-syndromic cases.
The remaining 5% of non-syndromic hearing loss is inherited through other patterns including X-linked (where the mutation is carried on the X chromosome), Y-linked (carried on the Y chromosome), and mitochondrial (carried in mitochondrial genes).
Risk Factors and Frequency for Genetic Hearing Loss
Hearing loss is the most common problem related to the body’s sense organs. For every 1,000 kids born, one has a hearing problem. This situation tends to get worse as children grow, with 2.7 out of every 1,000 children having hearing loss by the time they turn five. Currently, around 300 million people across the globe are believed to have hearing loss.
Signs and Symptoms of Genetic Hearing Loss
If a child has hearing loss, doctors usually conduct a thorough examination and ask questions about the child’s complete health records. They pay specific attention to details like:
- Conditions and environments during pregnancy (such as infections, trauma, medications, and other medical issues)
- The child’s family history to check if hearing loss is hereditary
- The results of the newborn’s hearing tests
Moreover, doctors carry out a full body check to see if there are any signs of syndromes that include hearing loss as a symptom. They particularly look at key systems that are often linked to hearing loss, such as:
- Eyes (ophthalmologic)
- Glands that regulate hormones (endocrine)
- Kidneys (renal)
- Heart (cardiac)
Testing for Genetic Hearing Loss
The Universal Newborn Hearing Screening program (UNHS) has greatly improved our ability to detect hearing loss in children at a much younger age, reducing the time of diagnosis from around 24-30 months to just 2-3 months. This process uses a sound wave test called Otoacoustic emissions (OAE), which is repeated if the child fails the initial checkup. If the child fails again, a test called the Auditory Brainstem Evoked (ABR) is done to confirm hearing loss.
Paying attention to your child’s hearing, especially at a young age is important because about half of all hearing loss in children is due to genetic reasons. Often, hearing screening programs may not be able to detect mild Sensory Neural Hearing Loss (SNHL), which involves damage to the inner ear. That’s where genetic screening comes in to identify kids who might have been missed in the regular check ups.
Doctors try to find out if there’s an environmental cause, signs and patterns indicating a syndrome, or a family history of similar hearing loss. If these are ruled out, genetic mutation testing is conducted for a gene called DFNB1 in the GJB2 gene, as this is the most common cause of hearing loss without any other symptoms. If your doctor suspects syndromic hearing loss, which includes additional health problems, specific gene testing is performed to confirm the syndrome. Genetic screening helps protect your child from potential hearing loss caused by certain antibiotics, and can vary based on the family’s health history.
A Computed Tomography (CT) scan may be used to look for any structural problems in the ear that could be causing hearing loss. For instance, a common finding in SNHL is Mondini dysplasia, which involves underdevelopment of a part in the inner ear, leading to progressive SNHL. If certain conditions are suspected, like enlarged passageways carrying fluid in the inner ear, your doctor may recommend genetic screening for Pendred syndrome, a disorder that can cause hearing loss.
Magnetic Resonance Imaging (MRI), a type of scan using strong magnetic fields and radio waves, is used to detect deformities in the inner ear and surrounding structures. It specifically helps to identify several conditions that cause hearing loss. Electrocardiogram, a test that measures your heart’s electrical activity, is also recommended in rare cases where a syndrome like Jervell and Lange-Nielsen syndrome, which causes heart problems and hearing loss, might be present.
Treatment Options for Genetic Hearing Loss
Treatments for considerable hearing loss include hearing aids, cochlear implants, and special devices that are implanted and use bone conduction.
Hearing aids, which are electronic devices that make sound louder, typically help patients with mild to severe hearing loss who still have good speech understanding and clarity. There are three types of hearing aids: behind the ear (BTE), in the ear (ITE), and those that fit in the ear canal. Children usually wear BTE hearing aids because as they grow, only the earpieces need to be remade, keeping the rest of the device the same. The ITE and canal types are less noticeable because they fit inside the ear.
For those with extreme hearing loss who don’t gain much benefit from hearing aids, cochlear implants can help. A cochlear implant involves an internal device and an external processor that works by sending electrical signals to the hearing nerve. While they don’t replace natural hearing, they can give access to a wider range of sounds and improve speech understanding with training and practice.
Children born with hearing loss who receive cochlear implants often show significant improvements in speech and language development. The earlier in life to implementation of these implants, the more likely it is to result in wider vocabulary. Theb best results are usually seen in those who lose hearing after learning language and those identified as deaf before age 2 who are implanted early. In fact, cochlear implants are now approved for infants as young as 9-months old who meet necessary criteria.
Lastly, people with certain types of hearing loss may benefit from implantable devices that use bone conduction. These devices send sound to the inner ear through bone conduction, bypassing the external and middle ear. They are either implanted under the skin or penetrate the skin. They can be particularly helpful when the middle or outer ears are not normal in shape and cannot be fixed with surgery.
What else can Genetic Hearing Loss be?
When a doctor is trying to determine the cause of hearing loss, they take into consideration both factors that a person is born with (genetic causes) and circumstances or conditions that develop after birth (acquired causes). Genetic causes are inherited from one or both parents, but there are other reasons why someone might be born with hearing loss. These include:
- Infections caught by the mother during pregnancy
- Abnormalities in the structure of the ear
- Medications that can damage the ears (ototoxic medications)
Looking carefully at all these possibilities helps the doctor figure out why the hearing loss has occurred.
What to expect with Genetic Hearing Loss
Genetic hearing loss can have significant impacts on a person’s social life, financial situation, and overall health. How well someone with this condition does over time, or their prognosis, largely depends on the cause. Prognosis can be greatly improved with early diagnosis and treatment. If too much time passes from when the person is diagnosed to when they start treatment, their abilities with speech and language may worsen. Their cognitive development, or how their brain grows and learns, could also be affected. If the person is exposed to more than one spoken language at home, this may also negatively affect their outcome.
But there’s hope on the horizon. As researchers continue to improve genetic testing and therapies, diagnostic abilities for syndromic hearing loss (a type of hearing loss that comes with other medical conditions) are improving. These advances could even potentially restore hearing in patients with certain conditions.
Possible Complications When Diagnosed with Genetic Hearing Loss
If a child’s hearing loss is not diagnosed and addressed promptly, it could negatively impact their life in several ways. They may experience delayed speech, problems communicating with their friends, feelings of isolation, reduced self-esteem, and limited educational and career options.
Potential Impacts:
- Delayed speech
- Difficulty in communication
- Social withdrawal
- Lower self-esteem
- Fewer opportunities for education and jobs
Preventing Genetic Hearing Loss
Most children who are deaf before they start to talk are born to parents who can hear. For these families, speaking and listening are often the preferred methods of communication, rather than sign language. However, some families choose to use sign language either because they are deaf themselves or they want to maintain the unique communicating culture of the deaf community. Doctors need to be aware of these preferences but they should also give patients and their families all the information about devices that can assist with hearing.
Doctors should explain the possible treatments to parents and set reasonable expectations for how much their child’s hearing might improve. The success of these treatments can depend on several things, such as what caused the hearing loss, when the diagnosis was made, and the treatment chosen. Hearing results can greatly differ based on these factors. Parents should be empowered to play a significant role in their child’s recovery and understanding all the financial implications of their health insurance.
Access to recovery services can be an expensive process which can make the best treatment harder to achieve, even in developed countries.
