Finding a cause

One of the first questions parents ask when their child is diagnosed with a hearing loss is “Why?” Mothers often join our online group and are worried that they did something before or during their pregnancy to cause their child’s hearing loss. But rest assured, this is extremely unlikely. Hearing loss can either be congenital or acquired. ‘Congenital’ means that the hearing loss was present at the time of birth, or occurred very soon after birth. An acquired hearing loss occurs after birth perhaps as a result of disease or injury. The terminology about causes of hearing loss can be rather confronting but, in reality, knowing the cause doesn’t usually change how the hearing loss will be managed.

Congenital hearing loss

About 1 in 1,000 babies are born with some degree of hearing loss. Congenital hearing loss may be due to either genetic factors or factors what occurred before, during or just after the baby was born.

1. Genetic factors

   Although 9 out of 10 deaf children are born to hearing parents, approximately 50% of hearing loss in children has a genetic cause. Genetic causes have to do with the baby’s genes. Genetic deafness may be inherited from one or both parents.
   
   
   • Syndromic hearing loss
     About 30% of children with genetic hearing loss have a “syndrome.” This means there are other features or conditions associated with the hearing loss. Examples are Pendred syndrome, which can include cochlear malformations such as enlarged vestibular aqueduct or Mondini malformations. There are over 400 different syndromes involving hearing loss. Each syndrome is relatively rare. 
     
   • Non-syndromic hearing loss
     The other 70% of children with genetic hearing loss have hearing loss that is “non-syndromic.” This means there are no other conditions linked with the hearing loss. Over 100 different genes have now been identified that directly cause or are associated with non-syndromic hearing loss.Genetic deafness may be present at birth or start later in life. It may also be stable or get worse over time.

2. Non-genetic causes
   
In about 25% of deaf children, their hearing loss is the result of another cause. Non-genetic causes of hearing loss include:
   
   • An infection that the mother might have had during pregnancy. Cytomegalovirus (CMV) is the leading cause of pre-lingual unilateral hearing loss in children in the United States ⁸.
   • Prematurity and low birth weight.
   • Some medications given to babies and young children to treat serious infections.
3. Idiopathic causes
   
In approximately 25% of deaf children, there is no known cause for their hearing loss.

Acquired hearing loss

Children can develop a hearing loss anytime after birth. This can be due to an illness such as meningitis, medications, recurrent severe ear infections or injury. One of the most common causes of acquired hearing loss in our online group is cholesteatoma.

Investigating the cause

Many medical tests can be carried out to try and find the cause of your child’s hearing loss. A cause is not found in over 50% of children investigated but it can be helpful to families to know what didn’t cause the hearing loss, e.g. you may find the cause isn’t genetic.

Families with a child with UHL are not always offered a full ‘aetiological investigation’, i.e. investigation of the cause of the hearing loss. Speak to your GP or ENT and let them know if you want to investigate the cause more fully. Tests you may request include blood and urine tests, imaging such as an MRI scan, genetic counselling and genetic testing.

For more information

• Medical assessments for children with permanent hearing loss
  http://www.aussiedeafkids.org.au/medical-assessments.html