Congenital hearing loss

Congenital hearing loss is a hearing loss present at birth. It can include hereditary hearing loss or hearing loss due to other factors present either in-utero (prenatal) or at the time of birth.

Genetic factors are thought to cause more than 50% of all incidents of congenital hearing loss. Genetic hearing loss may be autosomal dominant, autosomal recessive, or X-linked (related to the sex chromosome).

In autosomal dominant hearing loss, one parent who carries the dominant gene for hearing loss and typically has a hearing loss passes it on to the child. In this case there is at least a 50% probability that the child will also have a hearing loss. The probability is higher if both parents have the dominant gene (and typically both have a hearing loss) or if both grandparents on one side of the family have hearing loss due to genetic causes. Because at least one parent usually has a hearing loss, there is prior expectation that the child may have a hearing loss. Autosomal dominant congenital hearing loss can be attributed to such causes like Waardenburg Syndrome.

In autosomal recessive hearing loss, both parents who typically have normal hearing, carry a recessive gene. In this case the probability of the child having a hearing loss is 25%. Because both parents usually have normal hearing, and because no other family members have hearing loss, there is no prior expectation that the child may have a hearing loss.

In X-linked hearing loss, the mother carries the recessive trait for hearing loss on the sex chromosome. She can pass on the trait to males and female children, but usually only male children are affected.

There are some genetic syndromes, in which hearing loss is one of the known characteristics. Some examples are Down syndrome (abnormality on a gene), Usher syndrome (autosomal recessive), Treacher Collins syndrome (autosomal dominant), Crouzon syndrome (autosomal dominant), and Alport syndrome (X-linked).

Other causes of congenital hearing loss is that are not hereditary in nature include prenatal infections, illnesses, toxins consumed by the mother during pregnancy or other conditions occurring at the time of birth or shortly thereafter. These conditions typically cause sensorineural hearing loss ranging from mild to profound in degree.

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