Does genetics influence hearing loss?

In industrialized countries, approximately 6% to 8% of the population suffers from some form of hearing loss. Hearing loss can be caused by factors that cannot be changed, such as genetics, or others that we can prevent, such as overexposure to loud noises for long or short periods of time.

What is hearing loss?

Hearing loss encompasses a diverse group of disorders related to the decreased ability to hear certain sounds. Its causes can be environmental, genetic, or a combination of both. In addition:

• It can affect only certain frequencies (high or low tones) or be total.
• It can be temporary, caused, for example, by ringing in the ears due to exposure to loud noise, or permanent, due to irreversible damage to the mechanisms that enable hearing.

It should be noted that many cases of hearing loss are associated with age. This type of hearing loss or hearing impairment is known as presbycusis and is the most common, affecting approximately 40% of people over the age of 65.

Presbycusis is the “normal” aging of the ear, as opposed to deafness caused by a medical condition. Whatever the cause, it is clear that hearing loss has a major impact on the social lives of those who suffer from it. In the most severe cases, when the loss exceeds 40 decibels (dB) in the better-hearing ear in adults, and 30 dB in the better-hearing ear in children, it is considered disabling. More than 5% of the world’s population, 466 million people, suffer from hearing loss to this degree. Of this figure, 432 million are adults and 34 million are children. It is estimated that by 2050, one in ten people will suffer from hearing loss to one degree or another.

Difference between hearing loss and deafness

A person is considered to have hearing loss when their hearing threshold in both ears is less than 25 dB, and therefore they have difficulty hearing conversation or loud sounds.

Depending on its degree, hearing loss can be mild, moderate, severe, or profound. It can also affect one ear or both.

When hearing loss is between mild and severe, the person affected can usually communicate through speech and use hearing aids or cochlear implants as an aid.

When hearing loss is profound, the person hears very little or nothing at all, so they are considered deaf. They often communicate using sign language.

What factors increase the risk of hearing loss and deafness?

In addition to aging, situations such as chronic exposure to loud noises also contribute to hearing loss. Although there are factors that cause temporary hearing impairment, such as earwax, most types of hearing loss are irreversible.

Knowing the risk factors that can damage the inner ear is important in order to avoid those over which we have control, such as:

• Loud noises: these can damage the cells in the inner ear, either through constant exposure, as occurs in certain jobs (carpentry, factories, etc.), or through a sudden bang, such as a firecracker.
• Certain activities: exposure to aircraft turbine noise can cause immediate and permanent hearing loss. The continuous noise of motorcycle engines or listening to music at excessive volumes is also dangerous.
• Certain medications: some drugs used to treat malaria, drug-resistant tuberculosis, or certain types of cancer can cause temporary or permanent hearing loss or tinnitus, a type of ringing in the ears.

Risk factors beyond our control include:

• Certain diseases that can damage the cochlea, such as meningitis or measles.
• Aging: as we have explained, the passage of time can cause presbycusis.
• Genetics: there are genetic factors that predispose individuals to developing hearing loss, either in childhood or adulthood.

Classification of hearing loss

There are different ways to classify hearing loss:

• Unilateral or bilateral, depending on whether only one ear or both ears are affected
• Depending on when it occurs, it can be prelingual (before language development) or postlingual (after language acquisition, from the age of 4)
• Depending on the degree of hearing loss, it can be mild (threshold between 20 and 40 dB), moderate (between 40 and 70 dB), severe (between 70 and 90 dB), or profound (greater than 90 dB).
• Depending on the location of the lesion, deafness can be:
• • Sensorineural or perception: the alteration is in the inner ear or auditory pathway. Depending on when it occurs, it can affect language development in children.
  • Conductive or transmission: the alteration in sound transmission occurs in the outer ear and/or middle ear.
  • Mixed: the cause is both conductive and sensory.

Congenital and genetic hearing loss

Unlike acquired hearing loss, which develops at some point in life, congenital hearing loss is present from birth or shortly thereafter, and therefore before speech develops.

The incidence of congenital deafness in developed countries is 1-3 children per 1,000 live births. Approximately 50% of hearing loss is due to genetic factors; non-genetic causes may include:

• Rubella, syphilis, or other infections affecting the mother during pregnancy.
• Lack of oxygen at the time of delivery.
• Low birth weight.
• Severe jaundice (excess bilirubin in the blood) during the neonatal period, which can damage the baby’s auditory nerve.
• Inappropriate use of certain medications such as aminoglycosides, cytotoxic drugs, antimalarials, and diuretics.

Genetic hearing loss is classified into two main groups: syndromic and non-syndromic. Nearly 400 genetic syndromes have been described in which hearing loss is one of the symptoms, representing approximately 30% of cases.

Non-syndromic deafness, in which hearing loss occurs in isolation, without other symptoms, accounts for 70% of cases. Thanks to advances in scientific knowledge, the main genes responsible for this type of deafness are now known.

In the case of newborns, it is essential to detect the presence of genetic alterations associated with this condition in the first few months in order to implement a medical approach that allows for better integration of the child, through cochlear implants or speech therapy, among other measures.

Any type of hearing loss, to a greater or lesser degree, can have a negative impact on people’s quality of life due to the social isolation it often entails. As you have seen, certain cases of hearing loss and deafness are caused by hereditary factors. Knowing whether you are predisposed to these conditions is important in order to take preventive measures aimed at delaying their onset and minimizing the consequences of their development.

This is especially important in cases of congenital hearing loss, where the genetic component is greater. Veritas offers the myNewborn test, which allows you to personalize your newborn’s medical care from day one by analyzing 407 genes related to the onset of early-onset diseases, including the analysis of more than 60 genes associated with syndromic and non-syndromic deafness.