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Tay-Sachs Disease
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Description
Tay-Sachs disease, the most well known Jewish genetic
disease, is an inherited metabolic disorder. The basic defect in affected children
is the deficiency of an enzyme, hexosaminidase A. Without Hex A, a fatty substance
called GM2 ganglioside accumulates abnormally in cells especially in nerve cells
of the brain. This continual accumulation causes progressive damage to the cells.
There are two forms of this disease, the well known infantile-onset form and
a lesser known, late-onset or adult form designated "chronic GM2-gangliosidosis".
Symptoms
Infantile Tay-Sachs Disease
This disease is characterized by the onset of severe mental and developmental
retardation during the first four to eight months of life. The process begins
in the fetus early on the pregnancy, although the disease is not clinically
evident until the child is a few months old. The baby appears normal at birth
and seems to develop normally until six months.
The first signs of Tay-Sachs Disease vary and are evident at different ages
in affected children. Initially development slows, there is loss of peripheral
vision caused by an abnormality in the retina of they, and abnormal startle
reflex. By the age of two years most Tay-Sachs babies experience recurrent seizures,
and diminished mental status. The infant gradually regresses, losing skills
one by one.
Tay-Sachs Disease is fatal, and death occurs by the five to eight years of life.
Late
Onset of Tay-Sachs Disease - Chronic GM2-gangliosidosis
A late-onset form of hexosaminidase A deficiency occurs in adolescents and adults
of Ashkenazi Jewish ancestry. This disorder, called chronic (or adult) GM2-gangliosidosis,
or late-onset Tay-Sachs disease (LOTS), has been detected in over 30 individuals
from Ashkenazi Jewish families residing in both the United States and Israel.
Onset of the disease occurs during childhood or adolescence and is characterized
by poor coordination, tremor, and/or slurred speech.
Incidence
and Carriers
Both infantile and adult forms of Tay-Sachs Disease occur more frequently, though
not exclusively, in a defined population. A person's chances of being a Tay-Sachs
Disease carrier are significantly higher if he or she is of eastern European
(Ashkenazi) Jewish descent. Approximately one in every 27 Jews in the United
States is a carrier of the Tay-Sachs Disease gene. There is also a noticeable
incidence of Tay-Sachs Disease in non-Jewish French Canadians living near the
St. Lawrence River and in the Cajun community of Louisiana. By contrast, the
carrier rate in the general population as well as in Jews of Sephardic origin
is about one in 250.
The disease is transmitted through heredity. Both parents have to carry the
Tay-Sachs gene for there to be a possibility of transmission to their child.
If both are carriers:
· There is a One in Four chance that the
child will inherit the Tay-Sachs gene from each parent and have the disease
· There is a One in Four chance that the
child will inherit normal genes from both parents and be completely free of
the disease.
· There is a Two in Four chance the child
will inherit one of a Tay-Sachs gene from one parent and a normal gene from
the other parent, and in this case, be a carrier like the parents, but free
of the disease.
Treatment
There is no cure for Tay-Sachs disease,
treatment is symptomatic. However, researchers are focusing on finding a
cure. One venue that is being explored by scientists is enzyme
replacement therapy to replace the Hex-A lacking in babies with Tay-Sachs.
Another direction that researchers are focusing on is gene therapy which
would involve the transfer of a normal gene to replace the abnormal
gene.
Testing
Since there is no treatment for Tay-Sachs Disease, it is important for couples
in the risk group undergo genetic testing to determine if they are carriers.
Tay-Sachs Disease most often appears in families with no prior history of the
disease. The Tay-Sachs Disease gene can be carried without being expressed through
many generations. Before 1970, the only way to learn if one was a Tay-Sachs
carrier was to be the parent of a baby with Tay-Sachs Disease. Now, safe and
reliable carrier testing is available to identify Tay-Sachs carriers. Most important,
testing can identify carrier couples who are at risk for bearing a child with
Tay-Sachs Disease - before a tragedy occurs. With this vital information, couples
can explore the various options that will enable them to protect their families
from this devastating disease.
A simple blood test
can distinguish Tay-Sachs carriers from non-carriers. Blood samples can be analyzed
by either enzyme assay or DNA studies. The enzyme assay is a biochemical test
that measures the level of Hex-A in a person's blood. Carriers have less Hex-A
in their body fluid and cells than non-carriers. (Babies with Tay-Sachs disease
have a total absence of Hex-A in their cells.) The biochemical test
is able to detect all Tay-Sachs carriers of all ethnic backgrounds.
For information and referrals contact
Once pregnant there are prenatal tests that can diagnose Tay-Sachs in the fetus
before birth. These are Amniocentesis and Chorionic Villus Sampling. Amniocentesis
is done between the 15th and 16th week of pregnancy. A needle is inserted into
the mother's abdomen and a sample of the the fluid that surrounds the baby is
taken. In CVS a sample of cells from the placenta is retrieved by the doctor
during the 10th and 12th week of pregnancy, and tested for the presence of hex
A.
Resources
and More
National Tay-Sachs & Allied Diseases Association
2001 Beacon Street, Suite 204
Brighton, MA 02135
Toll Free: 800-906-8723
Telephone: 617-277-4463
Fax: 617-277-0134
Website:http://www.ntsad.org
Tay-Sachs Prevention Program
Thomas Jefferson University
1100 Walnut Street, 4th Floor
Philadelphia, PA 19107
Telephone:215-955-8320
Late-Onset Tay-Sachs Foundation (LOTS)
1303 Paper Mill Road
Erdenheim, PA 19038
Toll Free: 800-672-2022
Telephone:215-836-9426
Website:http://www.lotsf.org
Center for the Study and Treatment of Jewish Genetic
Diseases
at UPMC Health Systems
Community Tay-Sachs Screening Program
Toll Free 800-334-7980
Email:
National Foundation for Jewish Genetic Diseases Inc.
250 Park Avenue, Suite 1000
New York, NY 10017
Telephone 212-371-1030
Support Groups
Genetic Alliance, Inc.
4301 Connecticut Ave. NW, Suite 404
Washington, DC 20008
(202) 966-5557
www.geneticalliance.org
MD Junction
http://www.mdjunction.com/tay-sachs-disease
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