Genetics and Hearing loss

More than 5% of the world's population, including 34 million children, require rehabilitation to address hearing loss that causes disability, and it is expected that the number of people worldwide suffering from hearing loss will increase to about 700 million by the year 2050, according to the World Health Organization.

Disabling hearing loss occurs when the rate of hearing loss in the ear with the stronger hearing capability exceeds 35 decibels, and the likelihood of developing disabling hearing loss increases with age, with over 25% of those over 60 years old facing disabling hearing loss.
It is worth noting that most cases of hearing loss result from genetic factors that affect the child from birth, but they can also result from environmental factors or the interaction of genetic and environmental factors together.

In this article, we will shed light on genetic deafness, its symptoms, the importance of genetic testing in early detection, and the development of new effective treatments to overcome it.

How do we hear?

It all begins with a sound wave entering our ear through the auditory canal, causing the eardrum to vibrate. These vibrations pass from the eardrum through auditory ossicles in the middle ear, then they are captured by tiny hair cells in the cochlea to be amplified and transmitted to our brain via the auditory nerve, where they are interpreted into sounds that we can hear and understand.

The difference between hearing loss and deafness

Hearing loss refers to a decrease in hearing ability compared to normal levels, and its severity ranges from mild (ability to hear sounds at levels of 25-29 decibels) to moderate (hearing sounds at levels of 40-69 decibels) to severe (hearing sounds at levels above 70-89 decibels) or profound (inability to hear sounds lower than 90 decibels). Hearing loss can occur in one ear or both ears, leading to difficulty hearing high-pitched sounds or understanding speech.

Deafness, on the other hand, refers to the complete inability to hear, and individuals with deafness typically rely on sign language for communication.

Types of Hearing Loss

There are three types of hearing loss, each with its own treatment:

Conductive Hearing Loss

Occurs when sound cannot reach the cochlea of the ear, and it can result from several causes, including:

• Excessive earwax.
• Accumulation of fluids inside the ear or ear infection.
• Tumors.
• Congenital abnormalities, such as small ear canal size.

This type of hearing loss may be treated through middle ear implantation or bone conduction systems.

Sensorineural Hearing Loss

Sensorineural hearing loss results from damage to the hair cells in the cochlea or damage to the auditory nerve. The likelihood of developing this type increases with age, as the ability of the hair cells in the ear to regenerate decreases. Sensorineural hearing loss may also result from the following factors:

• Continuous exposure to loud noises.
• Congenital abnormalities.
• Inner ear infections.
• Brain trauma.

Sensorineural hearing loss can be treated through cochlear implantation, auditory electrical stimulation, or middle ear implantation. Additionally, researchers are currently exploring the possibility of using stem cell therapy to regenerate hair cells in the cochlea.

Mixed Hearing Loss

Mixed hearing loss combines conductive and sensorineural hearing loss, resulting from damage to the middle ear and eardrum due to infection. This type of hearing loss may require surgical intervention, but it is not always an effective treatment option.

Causes of Hearing Loss

Hearing loss can result from genetic factors, which are a major cause in about 50-60% of cases of hearing loss in children. Approximately 70% of genetic changes causing hearing loss are not the result of specific genetic syndromes leading to hearing loss, while about 30% of these genetic changes are due to inherited syndromes that cause hearing loss. Examples of such syndromes include Turner syndrome, Alport syndrome, Usher syndrome, Goldenhar syndrome, Charcot-Marie-Tooth syndrome, Binder syndrome, Garfield-Lang-Nelson syndrome, Stickler syndrome, Vardenburg syndrome, and Treacher Collins syndrome.

Hearing loss can also result from environmental factors, such as infections during pregnancy or diseases affecting the child that lead to hearing loss. Additionally, hearing loss can result from the interaction of genetic and environmental factors, such as receiving inappropriate treatment leading to complications due to genetic changes in the individual conflicting with this treatment.

Symptoms of Hearing Loss

Some of the prominent symptoms of hearing loss include:

1. Failure to respond to sound before the age of 4 months.
2. Inability to speak by the age of 1 year.
3. Speaking loudly.
4. Complete or partial loss of speech.
5. Social communication difficulties.

Hearing Loss and Genetic Therapy

A recent research team from the Harvard Medical School has succeeded in developing a new genetic therapy to treat a rare type of hearing loss caused by a mutation in the OTOF gene, responsible for producing the protein otoferlin, which transmits sound signals from the ear to the brain.

The concept of genetic therapy relies on modifying one of the most prominent viruses used in delivering a healthy copy of the gene to the body, known as adeno-associated virus, to transport a healthy copy of the OTOF gene to the inner ear.

This genetic therapy has proven its effectiveness in 5-6 children aged 1-7 years old, where they regained their hearing ability and the oldest among them managed to speak simple words again.

 

The Importance of Genetic Testing in Preventing and Early Diagnosis of Hearing Loss

Genetic testing significantly contributes to:

Early Diagnosis

Genetic testing helps identify the genetic causes of hereditary hearing loss early on through premarital and prenatal genetic screenings, exome sequencing, and comprehensive genetic testing (genomics) to determine if couples carry any genetic variations that could cause hereditary hearing loss in their future children and provide necessary recommendations. Newborn genetic testing can also be conducted to confirm diagnosis of hearing loss, aiding in developing appropriate treatment plans.

Family Planning

Genetic testing for prospective and married couples helps discover genetic variations that may cause hereditary hearing loss or other inherited diseases, increasing the likelihood of their children developing hearing loss in the future through premarital and prenatal genetic screenings or carrier screening to determine if couples carry any genetic variations that could cause hearing loss in their future children and provide necessary recommendations.

Development of New Treatments

Through genetic testing, more genes that lead to hearing loss or other unknown types of hearing loss can be discovered, forming a more comprehensive understanding of how these variations contribute to hereditary hearing loss and developing more effective treatment options.

Genetic Counseling

Genetic counseling guides appropriate actions and recommends comprehensive genetic testing based on the information provided about your and your family's health status. Genetic counseling also helps determine the likelihood of hearing loss recurrence in the family based on the degree of relatedness.

The role of a genetic counselor is not limited to pre-testing but also helps you understand the test results, providing necessary recommendations, guidance, and psychological support.

Enigma Genomics provides comprehensive genetic tests for hereditary diseases, such as premarital screening, which covers more than 550 hereditary diseases, Whole Genome Sequencing, which covers more than 7,500, and Whole Exome Sequencing, which covers 7,000 genetic diseases and others to help you in the journey of maintaining your health and the health of your family.