Causes of hearing loss – in brief

One of the first questions parents ask when their child is diagnosed with a hearing loss is “Why?”

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.

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 that occurred before, during or just after the baby was born.

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 Down Syndrome and Usher Syndrome. 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.

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 most common of these infections.
• Prematurity and low birth weight
• Severe jaundice at birth
• Some medications given to babies and young children to treat serious infections.

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. If a child develops a hearing loss after they have learned to talk, the hearing loss may be referred to as a ‘post-lingual’ hearing loss.

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References

• Deafness and Hearing Loss – Genetic aspects | Centre for Genetic Education
• Incidence, Prevalence, and Aetiology of Childhood Hearing Loss | Victorian Deaf Education Institute