Related
Links
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.
[Return to Top]
Date:
March 19, 2009
Content source: National Center on Birth Defects and Developmental
Disabilities
