Do you have good genes for hearing?
Genetics can play a significant role in our hearing health, with a wide variation in causes of hearing impairments across the lifespan. Of the 20,000 genes that make up who we are, it is estimated that at least 200 are required for the ear’s function and development.
Inheritance Patterns and Genetic Syndromes
The most common way congenital hearing loss is passed down in families is through parents each passing on a recessive gene, known as autosomal recessive inheritance. In these cases, inherited hearing loss is often caused by the Connexin 26 gene, which typically operates in a recessive manner. Additionally, genetic hearing loss can result from autosomal dominant inheritance, meaning that only one altered copy of the gene can cause hearing loss, even if there is a second working copy.
Furthermore, some genetic syndromes are characterised by hearing loss, meaning the hearing loss is a symptom of a broader health condition or syndrome. It is estimated that one in three children with genetic hearing loss has a syndromic cause, implying they may have or develop other symptoms. There are over 400 syndromes associated with hearing loss and deafness. For example, Down’s syndrome, Treacher Collins syndrome, and Usher syndrome are all conditions where hearing loss may be an associated symptom.
Other Genetic Influences on Hearing Health
Genetic hearing loss can also occur due to changes in the cell’s mitochondria, known as mitochondrial inheritance. This type of inheritance is only passed on from the mother, meaning a father cannot pass on mitochondrial conditions to his children. Some forms of sensorineural hearing loss are caused by maternally inherited deafness.
The final genetic cause of hearing loss is known as X-linked inheritance, which can involve either recessive or dominant X-linked variants. This type of inheritance affects males and females differently and is less common than other congenital causes of hearing loss. An example is progressive hearing loss caused by mutations in the POU3F4 gene.
Genetic Factors in Age-Related Hearing Loss
Aside from congenital causes, genetics can also contribute to hereditary factors leading to hearing loss. Age-related hearing loss, or presbycusis, has a significant genetic component. Studies have shown that genetics can influence our susceptibility to age-related hearing loss and its severity. Genetic variations can make some people more prone to age-related damage to the inner ear system.
Genetic Influence on Ototoxicity
Similarly, hearing loss can be caused by toxic medications and drugs, a condition known as ototoxicity. A person’s susceptibility to ototoxicity can be influenced by their genetics. Exposure to certain medications, chemicals, and environmental factors can damage the inner ear, leading to hearing loss. Genetic variations affecting drug metabolism can influence how individuals respond to these ototoxic substances. For example, if an individual is exposed to medication such as gentamicin for infections, they may be at greater risk of developing hearing loss if their genetic makeup makes them more susceptible to ototoxicity.
Genetic Predispositions to Tinnitus
Tinnitus is the perception of noise or ringing in one or both ears when no external sound is present. People often describe this sound as buzzing, hissing, ringing, or roaring. There are various causes of tinnitus, and genetics can play a role in predisposing individuals to it. Research suggests that genetic factors can make some people more vulnerable to developing tinnitus and may also influence the severity of the condition.
There are many genetic and hereditary factors that can contribute to congenital or progressive hearing loss. Understanding genetics, genetic testing, and counselling can lead to early diagnosis, better treatment, and greater prevention of hearing loss for many individuals. Identifying hereditary factors for hearing loss can also allow for access to early intervention and appropriate management strategies. In addition, ongoing research into the genetics causing hearing loss can lead to progress in developing therapies and interventions for preserving and treating hearing loss in the future.