Tay Sachs disease |
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Clinical signs |
Tay Sachs disease is a metabolic disorder transmitted by autosomal recessive inheritance
that causes the destruction of the infant's nervous system.
The infant appears completely healthy at birth and develops normally until about six months of age.
Then the first signs of the disease appear, marked by rapid general deterioration.
The infant loses the developmental achievements acquired up to that time, stops crawling or
turning, and loses his sight and the ability to grab and hold things with his hands.
Mental retardation develops a short time after the onset of the disease.
As the disease progresses, the infant also loses his ability to eat and sometimes his ability to smile.
Death usually occurs at about the age of two years.
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Types |
There is only one type.
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Is the disease treatable? |
No. Today, an infant with Tay Sachs disease cannot be treated effectively.
Therefore, the only way of coping with the disease is by prevention.
It is therefore important to know how the disease is caused.
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Inheritance pattern |
| Autosomal recessive |
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Penetrance |
| Full |
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What is the risk of recurrence in a subsequent pregnancy? |
For a couple who has already had an affected child, the risk is 25% in every subsequent pregnancy.
This also applies to a couple where both partners have been found to carry mutations for Tay Sachs disease.
When only one parent carries the abnormal gene, there is no risk that any of their offspring will
have the disease; however, in such families there is a 50% chance that the infant will be a carrier,
but he himself will be healthy, like the carrier parent.
The risk for more distant relatives depends on the number of affected individuals in the family,
the degree of relationship between the relatives and the affected individuals, consanguinity
between the parents, if present, etc. This risk is established within genetic counseling.
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Associated features that can be demonstrated in tests performed during pregnancy |
| There are no specific ultrasound signs and no associated defects.
The chorionic villus or amniotic fluid cells can be tested to measure the level of the enzyme
(hexosaminidase A) that is deficient in Tay Sachs disease - this enzyme test is exact.
It can be carried out in addition to the molecular test (described below).
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Molecular genetic information |
The gene for the disease
The gene responsible for producing hexosaminidase A.
Location
15q23.
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Genetic testing |
Diagnostic testing |
A direct test can be performed to identify the mutation in the gene by testing for the common mutations.
See: Testing the disease-causing gene for mutations that
are common in a specific ethnic group - autosomal recessive diseases.
In addition, the level of the enzyme deficient in Tay Sachs disease patients can be
measured, thus unequivocally diagnosing patients.
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Carrier testing |
Is the risk of being a carrier greater among Ashkenazi Jews?
Yes. Tay Sachs disease carriers are usually Jews of Ashkenazi origin.
Other communities are at lower risk. The carrier frequency in the healthy Ashkenazi
Jewish population is 1:30 and in one out of 900 Ashkenazi couples, both partners are carriers.
Do couples who already have healthy children need to be tested?
Yes, if they have not been tested previously, and are planning further pregnancies.
If they have been tested previously, the test need not be repeated.
Is it necessary to book an appointment or pay for the test?
There is no need to book an appointment in advance. The test is free of charge or financial undertaking.
What must a young couple do?
The first step is to carry out a test to determine whether the partners carry an abnormal gene
for Tay Sachs disease. For this, one of them must undergo a specific blood test.
If the woman is pregnant, the father is tested.
If the results of the blood test show beyond doubt that the subject does not carry an
abnormal gene for Tay Sachs disease, there is no risk that any of the couple's children will be affected.
However, if the test results are unclear, or the subject is found to be a carrier, the couple is
invited to come for a further test at the same center where the first test was performed,
and the partner is also tested. If this shows that the partner is also a carrier, there is a 25% risk
in every pregnancy of having a child with Tay Sachs disease.
Couples where both partners are carriers are invited to come for genetic
counseling in which they will receive an explanation about the disease and can discuss what
options are available.
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Fetal testing |
| As for diagnostic testing. |
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Can the disease be detected in pregnancy? |
| Yes, an affected fetus can be identified in the first trimester of pregnancy by
performing prenatal diagnosis (chorionic villus sampling
or amniocentesis). |
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What should be done if it is found that both partners are
carriers and that there is a risk that they may have a child with the disease? |
| Prenatal diagnosis carried out in every pregnancy will allow carrier parents to have
only healthy children who do not have Tay Sachs disease.
When prenatal diagnosis indicates that the fetus is affected, the pregnancy can be terminated using
medical methods. In cases where both parents are carriers, therefore, it is very important that
the mother undergoes prenatal diagnosis in every pregnancy in order to identify an affected fetus
in the early stages of gestation, even if the couple already has healthy children. |
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Blood testing centers: |
Ask your physician for the local screening center.
Details are available at all family health clinics and regional health bureaus.
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