Genetics of Hearing Loss: Can Hearing Loss Run In The Family?
The short answer is yes, hearing loss can be passed on from generation to generation. Genetic hearing loss is, in fact, the cause for about 50 per cent of hearing impairments in babies and young children. With about 400 known genetic causes for hereditary hearing loss and deafness, it’s worth taking a closer look at the genetics of hearing loss.
The auditory system consists of three parts: Sound is being picked up by the outer ear, passes through the ear canal and on to the middle ear, from there it moves through the cochlear which relays the information to the brain’s hearing centre. Each of these sections is affected by our genes.
Are you worried your child may be suffering from hereditary hearing loss?
Does hearing loss run in your family? A newborn hearing screen or hearing test for children will pick up on any hearing loss – genetically inherited or not. Prompt intervention can prevent negative effects on the speech and language development of babies and young children.
Don’t hesitate to chat to your GP or trusted Audiologist and schedule a hearing assessment as soon as possible!
Syndromic And Non-Syndromic Hearing Loss
There are two different types of genetic hearing loss: Syndromic and non-syndromic.
Syndromic hearing loss
|Syndromic hearing loss is a congenital hearing loss that occurs as the result of genetic mutations. It occurs as part of a cluster of medical problems. Syndromic hearing loss makes up 30 per cent of all genetic cases.|
There are many syndromes that can cause hearing loss such as Usher syndrome, Stickler syndrome, Waardenburg syndrome, Alport’s syndrome, and Neurofibromatosis type 2. In Alport’s syndrome, where hearing loss is commonly seen alongside kidney disease and eye abnormalities. The inner ear is usually the area causing hearing loss.
Non-syndromic hearing loss
|Non-syndromic hearing loss is a congenital hearing loss that occurs without other symptoms. It is the more common form of hereditary hearing loss, responsible for up to 70 per cent of genetic hearing losses.|
We speak of non-syndromic hearing loss when a hearing impairment occurs without other signs or medical problems other than hearing loss. Most genetically inherited loss is non-syndromic. Non-syndromic hearing loss occurs due to alterations of what is a ‘normal’ gene sequence, otherwise called gene mutation.
Although a family history of hearing loss is an important indicator, genetic deafness can be seen in children whose parents are not hard of hearing or otherwise have a family history of deafness.
Hearing loss doesn’t just affect “old people”. Learn more about the causes of hearing loss!
How is Hearing Loss Passed On?
Some gene mutations may not interfere with the health of an individual, others can be very disruptive. Gene mutations can also either be dominant or recessive.
Dominant gene mutation: A mutated gene is passed on by either parent, this gene is ‘stronger’ than the other unaltered gene inherited from the other parent.
Recessive gene mutation: Requires the child to acquire two altered genes, one from each parent, in order to be affected.
Mitochondrial inheritance is a special form of genetic inheritance which can affect hearing. The role of mitochondria is to provide energy for a cell, they have their own DNA which can also be mutated. These mutations usually affect functions that require a great deal of energy including the ears, eyes and heart. Mitochondrial genes are passed on via egg cells. The specific gene alteration and how many genes are affected, determined the severity of the resulting condition. A1555G mutation is an example of mitochondrial inheritance which increases an individual’s susceptibility for hearing loss induced by certain antibiotics.
Is Hearing Loss Always Passed On To Children?
It can be difficult to comprehend that a hearing loss or any other condition is “genetic” if they have never been seen in the family. Normal hearing babies can be born to a parent with hearing loss and vice versa. In fact, most babies with hearing loss are born to parents who can hear.
It is important to note that there are various complicated ways to inherit hearing loss.
Autosomal recessive hearing loss, for example, occurs when a child receives a hearing loss gene from each parent. Oftentimes, the parents themselves will have normal hearing. They’re what we call ‘unaffected carriers’. Two children born to the same couple have about a 25 per cent chance to have congenital hearing loss.
Autosomal dominant, hearing loss can affect each generation of a family or it can occur for the first time after a new gene mutation. Here, the chances of siblings having a hearing loss, vary greatly.
What are the risk factors?
Because we know that hearing loss runs in families, audiologists and other health professionals will routinely ask parents if there is anyone in the family who has a hearing loss.
Having a family member with hearing loss is considered a risk factor. Audiologists will identify babies with a risk factor and monitor them very carefully. They may be followed up more regularly than other babies.
How Can Hearing Loss Be Identified in Babies?
Hearing loss will be diagnosed by an audiologist. Audiologists test the hearing of people of all ages. All newborn babies will have their hearing screen shortly after birth. The audiologist will test a baby while it is sleeping. If a hearing loss is diagnosed, further testing is required to find out the cause of the hearing loss.
The audiologist will recommend a referral to an ENT (ear, nose and throat) specialist. The ENT will do a physical examination, take a close look at your family history, organise scanning of the temporal bone and order molecular genetic testing. Molecular genetic tests are available for many types of syndromic and non-syndromic genetic hearing loss.
Genes can be compared to a regular sequencing gene in order to detect whether there is a genetic mutation. Genetic testing is helpful when there is a known gene mutation leading to a condition (e.g. hearing loss), however, many unknown genes responsible for hearing loss might remain.
Genetics may help with predicting whether a child’s hearing loss may further deteriorate or remain steady. Genetic testing can also help determine which part of the hearing system may be affected. Both benefits of genetics testing will aid with treatment and management planning.
The genetic test involves looking at DNA to see if certain mutations are present. A DNA sample usually is taken from a small blood sample or cheek cells from inside the mouth. To get the cheek cells, a small, brush-like swab is rubbed inside the mouth.
What Are the Limits of Genetic Testing?
As not all the genes that cause hearing loss are known, even if a condition runs in a family, it might not be possible to find the mutation that causes it. Some tests are hard to do. For example, when the gene is bigger it is hard to study the whole gene. Sometimes, it is not possible to tell if a mutation has caused a condition, or if it is just a coincidence.
Alternative Causes of Hearing Loss in Babies and Children
There are many non-genetic causes of hearing loss. These causes make up around 50 per cent of all hearing loss in babies and young children. These include, but are not limited to:
- Certain infections the mother has during pregnancy
- Infections the newborn baby has
- Complications during or after birth
- Certain medicines
Sometimes genes and environment work together to cause hearing loss. For many babies, even after testing, the cause of hearing loss is still unknown.
Your Treatment Options
If you or your child are diagnosed with a permanent hearing loss that requires hearing aids or a Cochlear implant, you will be seeing your trusted audiologist for further advice. Intervention for genetic hearing loss can vary depending on which part of the auditory system has been affected and the degree of hearing loss.
Babies who are diagnosed with hearing loss will commonly see an audiologist who specialises in infants. This audiologist will confirm all the test results and establish the baby’s level of hearing loss. The child will then be referred to other audiologists and specialists.
An audiologist who specialises in paediatrics will fit and adjust the baby’s hearing aids. It is best to find a great local audiologist who will be able to help. They will monitor the child’s hearing and provide hearing aids and advice – as such, they will become an important part of your life. Regular hearing aid adjustments and maintenance will be required as the child grows and matures and the audiologist will perform all of these tasks.
Children who have been diagnosed to have genetic hearing loss are eligible to have hearing devices subsidised under a government’s hearing scheme. There is great emphasis on having your child fitted with the subsidised hearing devices in order to allow for less impact on language and educational development.
Aside from subsidised hearing devices, other assistive listening technology may also be provided. For more severely impaired hearing loss, your child may require a cochlear implant which helps stimulate affected inner ear hair cells, therefore sending sound to the brain’s hearing centre.
Hearing loss can be passed on from parents to their children, but it’s not always the case. Hereditary hearing loss can skip generations, or one sibling may have it, whilst the other has normal hearing. Genetic hearing loss can also occur after a spontaneous gene mutation.
Whatever the cause, genetic hearing loss can be challenging to diagnose as it is more often non-syndromic. Emphasis should therefore be put on early detection. If hearing loss affects you and your family, don’t hesitate to contact your local audiologist.
Hearing devices and assistive listening devices are commonly used to successfully manage genetic hearing loss. Assistive technologies and hearing solutions ensure that hearing loss has as little impact as possible on a child’s speech and language development.
Your audiologist will be able to help and guide you throughout the various hearing stages of your and your child’s life. It will be important to find an audiologist who makes you and your child feel at ease and who you both enjoy visiting.