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Hearing loss has many causes: some are environmental (such as certain infections in the mother during pregnancy, or infections in the newborn baby), and some are genetic. A combination of environmental factors and genes also could cause hearing loss. 

In about 30% of babies with a hearing loss, the loss is part of a syndrome, meaning that these babies have other problems. There are more than 400 syndromes that can cause hearing loss. The other 70% of cases are nonsyndromic, which means that the baby does not have any other problems. 

We are just beginning to identify which genes increase a baby’s chance of hearing loss. A recent and exciting discovery was the GJB2 gene. The GJB2 gene contains the instructions for a protein called connexin 26; this protein plays an important role in the functioning of the cochlea. The cochlea (the part of the ear that changes sounds in the air into nerve signals to the brain) is a very complex and specialized part of the body that needs many instructions to guide its development and function. These instructions come from genes. Changes in any one of these genes can result in hearing loss. 

About 40% of the newborns with hearing loss who do not have a syndrome, have a variation in the GJB2 gene in some populations. There are many different variations in this gene that cause a hearing loss. Most of these variants are called recessive, meaning that a person can have one usual copy of the gene and one of the variants and will have normal hearing function. (Every one has two copies of the GJB2 gene, one from each of their parents). However, a person with two variant copies of the gene, one variant copy inherited from each parent, will have hearing loss. This means that if both parents have a variant copy of the gene, they can have a child with hearing loss, even though both parents can hear. In fact, 90% of babies with hearing loss are born to parents who can hear.

Related Links: 

For more information about genes related to hearing loss and about genetic testing, contact a genetic counselor in your area.

Parent's Guide to Genetics booklet

For more information about how the ear works, see Promenade 'round the Cochlea (contains interesting pictures and graphics).

For more information about hearing and hearing loss, see the National Institute on Deafness and Other Communication Disorders.

For an overview of the genes involved in hearing loss, see Gene Clinics.

For more information about connexin-26, see the Online Mendelian Inheritance in Man website (this site contains a catalog of human genes and genetic disorders and can be a useful reference for health professionals): 

This guide from the U.S. Department of Health and Human Services explains about genes and genetic testing. 

The “Genetic Science Learning Center” has some information about basic genetics, genetic conditions and genetic counseling. 

This source from Cold Spring Harbor Labs is a tutorial about genetics. It is a little more in-depth than some of the other sites. 

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Date: April 04, 2007
Content source: National Center on Birth Defects and Developmental Disabilities