Connexin 26 Hearing Loss

It is estimated that half of all sensorineural hearing loss occurs on a genetic basis. However, most children who are born with significant hearing loss have two parents with normal hearing and no brothers or sisters with hearing loss. Until recently, there were few tests available to determine if a child in this situation had a genetic hearing loss. Genetic hearing loss was usually identified only if another sibling had a similar hearing loss, if either or both parents had hearing loss, or if the affected child had a known genetic syndrome in which hearing loss occurs in association with other findings. However, only a minority of children with hearing loss have immediate family members with hearing loss, or an identifiable syndrome. Therefore, the presence of genetic hearing loss could not be confirmed for most families. As a result, parents seeking to understand the cause of their child's hearing loss had to be told that a genetic cause remained a possibility but could not be proven.

At the present time, there is much ongoing research to determine which genes have the potential to cause hearing loss. Changes in a gene known as Connexin 26 (Cx 26) have been found to be responsible for half of all hearing loss that occurs on a genetic basis. Cx 26 is a gene that makes an important protein needed for function of certain populations of cells inside the inner ear. Changes in the building blocks that make up the Cx 26 gene may result in hearing loss, especially if inherited from both parents.

The majority of individuals with hearing loss secondary to Cx 26 have hearing loss in the severe-to-profound range. Therefore, Cx 26 is a major cause of deafness. Individuals with hearing loss secondary to Cx 26 do not have other clinical findings associated with their hearing loss. For example, they have normal X-rays of the inner ear and normal vestibular (balance) function. They do not have syndromes in which the hearing loss is associated with other disorders such as abnormalities of the kidney, heart or eye. (For example, individuals with Usher's syndrome lose their vision.)

Molecular genetic testing for hearing loss secondary to Cx 26 is now available (although not always paid for by insurance companies). The test involves taking a blood sample which is processed by a laboratory that examines the individual's Connexin genes in detail and looks for changes known to cause hearing loss. Identification of Cx 26 as the cause of a young child's hearing loss can significantly reduce the number of tests a physician might request in order to look for other causes. As a result of the availability of Connexin testing, many families are now having their question answered as to the reason for their child's hearing loss.



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