SLC26A4-related Permanent Hearing Loss

• Hearing screening helps find babies who have permanent hearing loss (PHL) or have a higher chance of developing it in early childhood.
• Finding hearing loss as early as possible allows children with PHL to get the support and services they need to learn language.

• Screening for PHL risk factors is part of infant hearing screening.
• Risk factor screening for PHL looks for the most common environmental (congenital cytomegalovirus) and genetic (variants in GJB2 and SLC26A4 genes) causes of childhood PHL.
• This screening is done using the dried blood spot sample collected for routine newborn screening.

• Variants (also called “mutations” or “pathogenic variants”) in the SLC26A4 gene can cause PHL. PHL can be present at birth (called congenital) or develop in early childhood. 
• SLC26A4-related PHL can affect some or all the sounds in the speech range and can cause hearing loss of any degree: mild, moderate severe or profound. It can impact one or both ears. SLC26A4-related hearing loss can often get worse (progressive). Sometimes we can predict what the hearing loss might look like based on the specific pathogenic variants identified.
• SLC26A4-related PHL runs in families in a way that is called “autosomal recessive”. Everybody has two copies of the SLC26A4 The gene makes a protein called pendrin, which plays a role in how the inner ear and thyroid work. When there are pathogenic variants in BOTH copies of the gene, it cannot do its job, and PHL can result.
• Pathogenic variants in the SLC26A4 gene can cause hearing loss only and be non-syndromic. The gene has also been associated with Pendred syndrome, which involves hearing loss and thyroid abnormalities.
• A person can have a pathogenic variant in only one copy of the SLC26A4 gene; this is called being a “carrier”. Carriers are not at increased risk for PHL. When both parents are SLC26A4 carriers, there is a 25% chance in each pregnancy to have a baby with two variants in the gene who has a higher chance of PHL.

• Newborn Screening Ontario (NSO) will contact you If your baby screens positive for SLC26A4-related PHL.
• A screen positive SLC26A4 risk factor screening result means there is an increased chance for the baby to have PHL that is present from birth or that develops in early childhood. The specific chances depend on the genetic variants detected.
• A hearing test with an Infant Hearing Program (IHP) audiologist is the only way to find out if a baby has permanent hearing loss.
• Rarely, SLC26A4 screen positive infants can develop thyroid imbalance. Thyroid screening is therefore recommended.
• The IHP audiologist will do several different tests to check a baby’s hearing. The IHP audiologist will do several different tests to check a baby’s hearing. These tests help determine if there is hearing loss, which sounds the hearing loss is impacting, how much hearing loss there is, and if the hearing loss is permanent or not.

• Baby has permanent hearing loss (PHL)
  • When PHL is identified, the IHP audiologist gives more information about the hearing loss. They explain what interventions, services, and supports the IHP offers to help.
  • NSO sends a referral to an Ear, Nose, Throat (ENT) doctor (also called an otolaryngologist).
• Baby does not have PHL
  • The IHP offers regular hearing testing during early childhood so that if PHL develops in the future, it is found as early as possible. This is called audiologic surveillance.
• Unclear if baby has PHL
  • Rarely, the IHP audiologist is not able to complete all the testing required to determine if PHL is present or not. If this happens, a follow-up appointment is made to complete the testing.

• Children can have very good language and education success with any degree of hearing loss. To achieve this hearing loss needs to be found as early as possible, and interventions put in place for baby at a very early age.
• The right intervention for any baby depends on the type of hearing loss and how big it is. Equally important is the family’s choice regarding language development. Baby’s local IHP team including Audiologist, Family Support Worker, and Language Development specialist, will help the family plan and start interventions.
• Interventions often include regular hearing testing, hearing aids or cochlear implants, spoken language or sign language therapy.

Genetic hearing loss is the leading cause of PHL in young children. That means that a lot is known about how to help these children and their families have the best outcomes for language, social and education goals. Baby’s local IHP team will provide families with support, resources, and lots of information tailored to that baby’s particular needs. But for all children with PHL finding hearing loss early, putting an intervention in place early, and following that intervention plan closely gives the best chance for the best outcomes.