Genetic Hearing Loss

Hearing loss is the most familiar sensory defect present in humans, affecting more than 10 percent of people age 65 and older. In many cases, hearing loss is caused by multiple factors, including genetic and environmental causes. Single-gene mutations can often lead to hearing loss. Genetic factors make some people more susceptible to hearing loss as their genes make them more predisposed due to ageing, loud noises, infections, or drugs. It is estimated that between 30 and 60 percent of age-related hearing loss is due to genetics.

There are two primary forms of hearing loss. These include sensorineural hearing loss and conductive hearing loss – as well as a combination of the two. Sensorineural hearing loss begins when there is harm done to the cochlea inner ear or to nerve pathways that run from the inner ear to the brain. Sensorineural hearing loss reduces the ability to hear faint sounds. Common causes include illnesses, aging, certain drugs, genetics, head trauma, malformation of the inner ear, and loud noises. Conductive hearing loss is caused when sound is not properly conducted through the outer ear and into the eardrum. Common conductive hearing loss causes include allergies, ear infection, benign tumors, and infection in the ear canal, impacted eardrum, swimmer’s ear, or presence of a foreign object.

Syndromic Versus Non-Syndromic

Genetics is one of the most common hearing loss causes, accounting for approximately 60 percent of deafness occurring in infants. An average of three in every 1,000 babies is born with hearing loss or born deaf. Genetics is also one of the leading hearing loss causes in the elderly. Inherited genetic defects can occur at any point in a person’s life, leading to sudden hearing loss. These same defects can also cause a person to become deaf.

Syndromic: Syndromic refers to a hearing impairment associated with clinical abnormalities. Out of all genetic-related hearing loss, syndromic makes up 15 to 30 percent. More than 400 syndromes are known to include some type of hearing problem. These can include syndromes transmitted in Mendelian or monogenic, syndromes due to chromosomal anomalies, syndromes due to multi-factorial influences, or syndromes due to a combination of these.

Non-Syndromic: Non-syndromic refers to a hearing impairment that accounts for the majority of genetic-related hearing loss, nearly 70 percent. Autosomal-dominant genes account for up to 20 percent while autosomal-recessive inheritance is responsible for more than 80 percent of non-syndromic cases. Less than two percent of all cases are caused by mitochondrial genetic and X-linked malfunctions.

During the last decade, technological advances in genetics and molecular biology have developed our understanding of the function and pathology of the cochlea, or inner ear. Researchers now have a better grasp of hearing loss causes and what genetic factors lead to gradual and sudden hearing loss. This research is also helping the deaf and hard-of-hearing find more efficient treatment for better hearing. Screening tests are now available for those who have suffered gradual or sudden hearing loss which can provide alternatives for their hearing problems, such as assistive devices like hearing aids.