Tay-Sachs disease is a rare fatal disease, caused by a deficiency of the enzyme hexosaminidase A, which is used to break down fatty substances in the brain and nervous system.
Both parents each contribute a chromosomeOne of the structures within the nucleus of a cell that transmits genetic information. Each of the chromosomes contains a double strand of the helical nucleoprotein deoxyribonucleic acid (DNA). Chromosomes occur in 23 pairs in every human cell.
Visit our comprehensive glossary for more pregnancy terms and definitions. to the gene code that produce the enzymeA protein produced by the body's cells which catalyzes chemical reactions in organic matter. While most enzymes catalyze reactions within cells, digestive enzymes, which are produced in much larger quantities, act outside of cells within the digestive tract.
Visit our comprehensive glossary for more pregnancy terms and definitions.. If one parent is lacking the chromosome they are a carrier of the disease. If both parents are carriers, the baby has a twenty five percent (1 in 4) chance of developing the disease.
Tay-Sachs screening was developed in the early 1970s and allows parents to understand the risk of having a child with Tay-Sachs disease. Many families don't yet know if they have a history of the disease, because screening is still relatively new, and their parents, uncles and aunts were not tested for carrier status. The test also screens for a related enzymeA protein produced by the body's cells which catalyzes chemical reactions in organic matter. While most enzymes catalyze reactions within cells, digestive enzymes, which are produced in much larger quantities, act outside of cells within the digestive tract.
Visit our comprehensive glossary for more pregnancy terms and definitions. called hexosaminidase B. A deficiency of both hexosaminidase A and hexosaminidase B results in a very rare and serious form of Tay-Sachs called Sandhoff's disease.
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Tay-Sachs screening is performed on a blood sample of the mother. The amount of the enzyme hexosaminidase A and hexosaminidase B is tested, and the results are analyzed. If the mother is a carrier, the father is also tested for carrier status.
If both parents choose to have a child, the fetus can be screened for Tay-Sachs disease, by analyzing the amniotic fluidThe liquid, which is produced by both the fetal membranes and the fetus that surrounds the baby during pregnancy. The liter of fluid at term serves to protect the fetus during pregnancy and also provide active chemical exchange.
The amniotic fluid consists of maternal and fetal plasma in varying concentrations. The pH of the fluid is almost neutral and clear, although lipids and desquamated fetal cells can make it cloudy.
Visit our comprehensive glossary for more pregnancy terms and definitions.. The sample is collected either by amniocentesis or chorionic villus sampling. The umbilical cord blood can also be tested immediately after delivery.
This disease, unfortunately, is most common among people of Ashkenazi Jewish ancestry. All partners of Ashkenazi Jewish heritage should be screened, since about 3.7% (1 in 27) carry the recessive gene, which is also high among the French-Canadian population.
The incidence of carrier status in people who are not of Ashkenazi Jewish heritage is 0.67% (1 in 150). Carriers of the recessive gene are perfectly healthy and show no signs of the disease, and cannot get the disease. If one parent is a carrier of the disease, the child will inherit carrier status.
There are few, if any, risks associated with this test.
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The test should be performed before conception. If the pregnancy is unplanned, the test can be performed using chorionic villus sampling or amniocentesis at the appropriate times.
The normal combined total values of hexosaminidase A and hexosaminidase B vary between 10.4 and 23.8 units per liter depending on the laboratory's method of testing. Of that, hexosaminidase A forms about 56% - 80% of the total. A carrier of Tay-Sachs has about half the normal value of hexosaminidase A. The disease is present if hexosaminidase A is lacking. In rare cases, both hexosaminidase A and hexosaminidase B are lacking resulting in a severe form of Tay-Sachs disease called Sandhoff's disease.
If the screening is done before conception you should seek genetic counseling. Depending on your beliefs, adoption may be the best option for you. Others may decide artificial insemination by a non-carrying donor is more suitable. If you decide to have children, the fetus can be tested in utero using chorionic villus sampling or amniocentesis.
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