Is hearing loss hereditary?

Is hearing loss hereditary? It’s an important question to ask, especially if you have a family history of hearing loss and you have concerns about your children’s hearing health. The reality is that around four in every 1,000 babies are born with hearing loss according to the Ontario Ministry of Children and Youth Services. Hereditary factors play a role in at least 60% of those cases.

But not all genetic hearing loss shows up at birth. Some inherited hearing loss conditions develop over time. Research indicates that a large percentage of hearing loss among the elderly is due to these inherited genetic factors.

The role genetics play in the makeup of each human being is incredibly complicated. Genes determine everything from hair, eye, and skin colour to body type and height. There are large gaps in our understanding of genes and we don’t always know why a child might be born with hearing loss. But there are four common pathways for inherited hearing loss. These include:

  1.  Autosomal Dominant Inheritance—only one copy of the gene for hearing loss needs to be present for hearing loss to occur.
  2. Autosomal Recessive Inheritance—the child needs to inherit one copy of the hearing loss gene from both parents for hearing loss to occur.
  3. X-linked Inheritance—the hearing loss gene is linked to the sex chromosome and will more likely affect males.
  4.  Mitochondrial Inheritance—affected mothers can pass on hearing loss through the mitochondria DNA.

Will my children have hearing loss?

You are probably reading this article because you have concerns about your children inheriting a hearing loss condition. The study of genetics can help predict the likelihood of an inherited condition being passed on but there are still many unknowns.

Let’s look more closely at those four common pathways for inherited hearing loss to understand how they work.

  1. Autosomal Dominant Inheritance

It only takes one copy of the gene for hearing loss from one parent to cause hearing loss in the child.  If one parent has a copy of this gene there will be a 50% chance of the children developing the condition too. If a parent has two copies of the damaged gene then all of their children will have hearing loss. Autosomal dominant genes cause around 20% of genetic hearing loss. Males and females have an equal chance of experiencing hearing loss due to autosomal dominant genes.

Waardenburg syndrome is a common autosomal dominant hearing loss condition. It tends to trigger abnormalities in the eyes, skin, and hair as well as trigger hearing loss ranging from mid-frequency hearing disorders to complete deafness. Waardenburg syndrome causes around 2 to 5% of congenital hearing loss cases (1 in 40,000 people).

  1. Autosomal recessive inheritance

Recessive traits are not usually visible meaning that the parents may have the gene but don’t display any of the symptoms. We call these parents, ‘carriers’. Although they may not show any signs of the disorder, if both parents carry the genetic abnormality, their children will have a 1 in 4 chance of developing hearing loss.

Recessive genes can jump a generation so although you carry the gene it may not show up until your children have children. Recessive genes are the most common cause of hereditary hearing loss causing around 80% of inherited hearing loss.

Usher syndrome is a common recessive gene abnormality. Children with Usher syndrome are often born with hearing loss and will usually develop a serious eye condition causing blindness as well. The GJB2 gene is one of the genes typically responsible for autosomal recessive gene hearing loss. It is possible to screen for this type of genetic abnormality as well as for other hearing loss genes.

  1. X-linked inheritance

If the mother has this genetic abnormality, there is a 50% of passing it on to her male children. This is because this mutation affects the female X chromosome. The female has two X chromosomes and acts as a carrier.  A male will have only one copy of the X chromosome and so if he inherits the damaged chromosome from his mother he will display the hearing loss trait.

Fortunately, the X-linked recessive gene causes fewer than 2% of genetic hearing loss cases and it does not usually lead to complete hearing loss.

  1. Mitochondrial inheritance

Only females can pass on mitochondrial genetic mutations. This type of genetic inheritance can trigger diabetes as well as late or early onset hearing loss. Hearing loss due to mitochondrial inheritance is relatively rare.

Genetic testing

You can test your DNA for these mutations but the results can have some serious implications. Firstly, the fact that you may not carry or display any of the genetic abnormalities that commonly lead to hearing loss does not guarantee that your children won’t have hearing loss. This is because genetic abnormalities may show up in very different ways that the tests can miss.

Secondly, genetic testing may reveal sensitive information about other members of your family. It may reveal an adoption or a different biological father. Thirdly, the results may trigger strong emotional reactions that may surprise you.

So, it’s important to weigh up the risks before you decide to undergo extensive testing.

Can non-hereditary conditions cause hearing loss in babies?

Yes, non-genetic issues cause around 30 to 40% of congenital (at birth) hearing loss. Such issues include:

  • Ototoxic medication given to the mother can damage the auditory nerve in the fetus
  • Premature birth—extremely low birth weight is a risk factor associated with hearing loss
  • Infections in the mother during pregnancy such as toxoplasmosis, cytomegolavirus, herpes simplex or German measles
  • Birth complications such as lack of oxygen or other trauma can damage the baby’s hearing
  • Drug or alcohol abuse or smoking during pregnancy can cause heating damage in the fetus

Hearing loss can have a particularly serious impact on the social and intellectual development of young children. If you suspect your child has hearing loss you must get their hearing tested. Hearing tests are even available for young babies. Be on the lookout for common hearing loss symptoms such as developmental delays.

Early intervention will make all the difference for your children so it’s important to visit a qualified audiologist. The wide range of hearing aids combined with modern technology can transform the way your child experiences the world.