There are many different risk factors for childhood permanent hearing loss (PHL). Some are genetic (caused by changes in genes) and some are environmental, such as exposure to certain infections or medications.
What genetic risk factors are included in risk factor screening for PHL?
More than half of all childhood hearing loss has a genetic cause and many different genes are known to be related to hearing loss.
Risk factor screening for PHL looks for some of the most common genetic differences (also called mutations or pathogenic variants) in the GJB2, GJB6 and SLC26A4 genes that can cause hearing loss. A mutation or pathogenic variant is a difference in a gene that either makes the gene not work, or causes the gene to work differently. These three genes all provide instructions to make proteins that are important to the development of the inner ear or cochlea. The SLC26A4 gene is also involved in the development of the thyroid (a gland found in the neck region which makes important hormones the body needs).
If you are interested in learning the specific genetic mutations that are included in risk factor screening for PHL, please visit the genetic risk factor screening panel page on our website.
What does a “positive” genetic risk factor result mean?
A positive genetic risk factor screening result means that there is a high risk for PHL because at least two mutations in one of the genes tested were identified. Babies with a positive genetic risk factor screening result will have a hearing (audiology) assessment with an Infant Hearing Program (IHP) audiologist to determine whether PHL is present.
Carrier status for PHL will not be routinely reported but is available upon request from a parent/guardian or health care provider on their behalf.
How does permanent hearing loss (PHL) run in families?
Hearing loss can be inherited in different ways, depending on the genes and mutations involved. The genetic risk factor screen specifically looks for autosomal recessive hearing loss due to selected mutations in the GJB2, GJB6 and SLC26A4 genes.
“Autosomal” means that the mutations can affect both boys and girls. People with only one copy of an autosomal recessive mutation are less likely to have PHL and are called “carriers”. If two carriers have a child together, there is a 25% (1 in 4) chance that the baby will get two copies of the mutation and, therefore, be at high risk for PHL.
How do I request carrier status for PHL?
If only one mutation in a gene tested through risk factor screening is identified, this result will not be routinely reported; however, this information will be disclosed upon request of a parent/guardian or health care provider on their behalf. There are pros and cons to learning a child’s carrier status and it is a personal decision. We recommend that parents/guardians interested in requesting this information review their decision with a health care provider in advance.
Please contact via e-mail at newbornscreening@cheo.on.ca or by phone NSO at 613-738-3222 if you would like to request a child’s carrier status.