The Genetics of Infant Hearing Loss
Related Links Presentation Abstracts
About one in
every thousand newborn babies has hearing loss. 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.
For help finding a genetic counselor in your area, see The National Society
of Genetic Counselors: http://www.nsgc.org/resourcelink.asp
For more information about how the ear works, see Promenade 'round the
Cochlea (contains interesting pictures and graphics):
http://www.iurc.montp.inserm.fr/cric/
audition/english/index.htm
For more information about hearing and hearing loss, see the National
Institute on Deafness and Other Communication Disorders: http://www.nidcd.nih.gov/health/hb.htm
For more information about genes and how they work, see The Cooperative
Research Centre’s website: http://www.genecrc.org/ Their “Learning
Centre” and their “Kids Only” pages have good basic genetic information.
For an overview of the genes involved in hearing loss, see Gene Clinics:
http://www.geneclinics.org/profiles/
deafness-overview/details.html
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): http://www3.ncbi.nlm.nih.gov/Omim/
For more information about other genes involved in hearing loss, see the
Hereditary Hearing Loss Hompage: http://dnalab-www.uia.ac.be/dnalab/hhh/index.html
Genetics of Congenital Hearing Impairment provides information and abstracts from the June 7, 1999 conference. Hosted by the Centers for Disease Control and Prevention and Gallaudet University.