Genetic Testing for Hearing Loss | Frequently Asked Questions

Genetic hearing loss is related to the passage of genes that cause hearing loss through the family. Your child’s hearing loss may be genetic, even if no other people in your family have hearing loss.

How Hearing Loss Is Genetic

A gene is a packet of information that tells our bodies to do a specific job. Many genes work together to tell the ear to hear. Genes are made of a chemical called DNA (deoxyribonucleic acid). There are about 20,000-25,000 genes in our bodies. At least 100 of these genes play a role in hearing. In our bodies, genes come in pairs. One member of each pair is inherited from a child’s mother, and one from a child’s father. Most of the time, both genes within a pair are nearly identical. Sometimes, a small change occurs within a gene that may be harmful. A change in one of the many genes that control the functioning of the ear may lead to hearing loss.

Common Patterns of Inheritance of Hearing Loss

• Autosomal Recessive Inheritance (AR): Most genetic hearing loss in childhood is inherited as an AR condition. AR conditions arise when both members of a gene pair fail to work properly. In these families, a child inherits a change that causes hearing loss from each parent. The parents can hear because they have both the working gene, and the non-working gene that causes hearing loss. These parents are described as carriers of hearing loss. In these families, each child has a one-in-four chance of hearing loss.

A carrier of a genetic disorder is someone who has a change in one of his or her genes without showing symptoms of the disorder. When two people carry a genetic disorder they can pass the disorder on to their children. So, it is possible to have a child with genetic hearing loss, even when parents are hearing and have no family history of hearing loss.

• Autosomal Dominant Inheritance (AD): In some families, parents or other relatives do have hearing loss. Most genetic hearing loss that occurs in adolescence or adulthood is inherited as an AD condition. AD conditions arise when a single member of a gene pair fails to function properly. In these families, a child inherits a change that causes hearing loss from only one parent. Typically, that parent has hearing loss as well. In these families, each child has a one-in-two chance of hearing loss, and a 50 percent chance of hearing.

Hearing loss may also be passed along in a family as X-linked recessive or mitochondrially inherited traits. Your genetic counselor can explain these in more depth.

Genetic testing is the complex process by which the more common genes related to hearing loss are analyzed in the laboratory. A small sample of blood (or other tissue) is needed for analysis. Cincinnati Children’s tests for 23 genes associated with hearing loss. About 80 percent of the genetic causes of hearing loss are identified by these tests.

We believe that all children with inner ear hearing loss may benefit from genetic evaluation and testing. Genetic test results may:

• Determine the exact cause of your child’s hearing loss
• Reduce or eliminate the need for other invasive and costly medical tests
• Provide you with information about your child’s future hearing and other potential medical complications
• Help you and your child’s physician to determine the best treatment and long-term medical management for your child
• Provide you with information about your chance of having another child with hearing loss

The ear has three main parts: outer, middle and inner.

The outer ear (the part you can see) opens into the ear canal. The eardrum separates the ear canal from the middle ear. Small bones in the middle ear help transfer sound to the inner ear. The inner ear contains several channels of fluid and specialized cells that detect fluid motion. These cells are connected to the auditory (hearing) nerve, which leads to the brain.

Any source of sound sends vibrations or sound waves into the air. These funnel through the ear opening, down the ear, canal, and strike your eardrum, causing it to vibrate. The vibrations are passed to the small bones of the middle ear, which transmit them to the fluid of the inner ear. Here, the fluid vibrations become nerve impulses and go directly to the brain, which interprets the impulses as sound (music, voice, a car horn).

If a problem arises in the outer or middle portion of the ear, a conductive (or mechanical) hearing loss (CHL) is present. Common causes of CHL are fluid in the middle ear from ear infections or an ear plug. If the inner ear or hearing nerve is damaged, a sensorineural hearing loss (SNHL) develops. The common forms of SNHL are from genetic (hereditary) factors or infections (i.e., meningitis). In general, CHL can be corrected with medicine or surgery, while SNHL is usually not reversible.

Complete medical consultation and genetic counseling is available through the combined efforts of the Ear and Hearing Center and the Division of Human Genetics (513-636-4760, option 1) at Cincinnati Children’s. For questions, contact us.

The American Society of Human Genetics recognizes that genetic testing is an integral part of the evaluation of a child with nonsyndromic hearing loss and has developed specific guidelines for incorporating genetic testing into your clinical practice [Genet Med 2002:4(3) 162-171].

Genetic test results may provide:

• Accurate determination of the etiology of the patient's hearing loss
• Reduction or elimination of the need for further invasive and costly diagnostic tests
• Basis for prognostic information about future hearing and potential medical complications
• Guidance regarding treatment and long-term medical management, particularly in the young infant
• Definitive information on which to base genetic counseling of families

Most insurance companies cover genetic testing of patients with hearing loss. Genetic testing early in the evaluation process may actually reduce costs related to the diagnostic evaluation [Otology and Neurology (2005) 26:610-615].