By Yishane Lee
Genetic causes account for roughly half of hearing loss cases in infants, according to the Centers for Disease Control and Prevention. Many cases of progressive hearing loss that occur after infancy and childhood also have a genetic component.
At least 1,000 mutations in 64 genes linked to hearing loss have been identified. Thanks to rapid advances in genetic sequencing, identifying virtually all the genetic causes of hearing loss may occur within the decade, according to a recent report in the journal Genetic Testing and Molecular Biomarkers.
Researchers are using “targeted resequencing” to locate gene mutations in certain regions in the human genome that are linked to diseases much more quickly than sequencing the entire genome. In our Fall 2013 issue of Hearing Health magazine, Xue Zhong Liu, M.D., Ph.D., reviews the advances in sequencing technology and how this will affect the future treatment of hearing loss.
Because genetics can play such a significant role in hearing loss, genetic testing can answer questions you have about the cause of your or a loved one’s hearing loss. If the testing uncovers a mutation, it can help explain the hearing loss, its severity or progression, and whether other symptoms may become apparent. For instance, a person with Usher syndrome has not only hearing loss but also eventual blindness. You can proactively take steps to manage treatment and outcome. Knowing the genetic cause of a hearing loss can also help you predict whether the condition will be passed along to your children, or whether the children of other family members may have the condition.
Last summer, Hearing Health magazine presented an overview of genetic causes of hearing loss, including Connexin 26 disorder. This is the most common cause of congenital hearing loss not related to a syndrome (with other symptoms, such as a thyroid problem). Mutations in the GJB2 gene affect development of the cochlea in the inner ear. Everyone carries two copies of the GJB2 gene (which encodes the protein connexin 26), and the mutations are usually recessive. So, two parents with one mutation each can have normal hearing. But if their child gets two faulty copies of the gene, the child will have a hearing loss. In fact, the majority of children born with hearing loss have normal hearing parents.
There are limits to genetic testing, however. For one thing not all the genes are known—yet. Also, a positive result for a mutation does not necessarily mean a person will get the condition associated with the mutation. And a negative result doesn’t mean you won’t get the particular condition, too—it may be that a different mutation in the same gene wasn’t detected, or there could be another mutation in a different gene that may cause the condition.
We have compiled a list of several dozen genetic testing centers nationwide that have specialized testing for hearing loss. Find a testing center near you.