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Late-onset forms of Sandhoff disease are rare and appear to share many of these symptoms.
Is there any treatment for these diseases?
There is currently no treatment to prevent these diseases from running their course. Affected individuals can be made as comfortable as possible and given other supportive care.
Researchers are investigating whether stem cell transplants could help babies with classic Tay-Sachs and Sandhoff diseases. Stem cells are immature blood cells that produce all other kinds of blood cells. Stem cells are obtained from umbilical cord blood or from the bone marrow of a donor. Unfortunately, stem cell transplantation has not yet been successful in stopping or reversing brain damage in Tay-Sachs or Sandhoff diseases, and this treatment poses a high risk of death in affected babies (NINDS, 2007; NINDS, 2009).
Researchers also are studying the effectiveness of drug treatments (including a drug called miglustat, which is approved by the Food and Drug Administration to treat a related disorder) to help reduce the build-up of fatty substances in brain cells in individuals with these diseases (National Tay-Sachs and Allied Diseases Association, Inc., 2009).
Who is at risk for Tay-Sachs and Sandhoff diseases?
Tay-Sachs disease occurs most frequently in descendants of Central and Eastern European (Ashkenazi) Jews. About 1 out of every 30 American Jews carries a mutation in the gene that codes for hex A (Kaback, 2006; American College of Obstetricians and Gynecologists (ACOG), 2005). Some non-Jewish individuals of French-Canadian ancestry (from the St. Lawrence River Valley of Quebec) and members of the non-Jewish Cajun population in Louisiana and the Old Order Amish in Pennsylvania also are at increased risk (Kaback, 2006; American College of Obstetricians and Gynecologists (ACOG), 2005). Individuals in other ethnic groups in this country have about a 1 in 300 chance of carrying a mutation in this gene (Kaback, 2006; American College of Obstetricians and Gynecologists (ACOG), 2005).
Sandhoff disease can occur in any ethnic group, though it is uncommon. Individuals not of Jewish ancestry are more likely than those of Jewish ancestry (1 in 600 vs. 1 in 1,000) to carry one of the gene mutations that cause Sandhoff disease (Online Mendelian Inheritance in Man #268800, 2009).
How are the diseases transmitted?
All forms of Tay-Sachs and Sandhoff diseases are inherited. Tay-Sachs disease is caused by mutations in a gene on chromosome 15 that codes for hex A. Sandhoff disease is caused by mutations in a gene on chromosome 5 that codes for hex B. Both diseases are passed on through parents who carry one of these mutations. A carrier does not have the illness. However, when two carriers become parents:
If only one parent is a carrier, the couple’s children cannot inherit the disease. However, each child has a 50-percent chance of inheriting the gene mutation and being a carrier.
Carrier screening is commonly performed before or during pregnancy for adults in populations who are at risk for these disorders.
How can people find out if they are carriers?
An individual can take a test that measures the amount of hexosaminidase in the blood. Tay-Sachs carriers have about half as much of hex A as noncarriers, but this is plenty for the carrier’s own needs. Similarly, carriers of Sandhoff disease have reduced but adequate amounts of both hex A and hex B.
A blood sample can be used to perform DNA-based genetic testing for known mutations in the hex A and hex B genes. Genetic testing may be recommended if the results of the carrier screening test are uncertain.
Carrier screening is available from a genetic services center or clinic. A health care provider can provide referrals to local sites where testing is available, as can the National Tay-Sachs and Allied Diseases Association.Trained genetic counselors explain test results so that individuals know whether or not their children are at risk for the disease.
Can these diseases be diagnosed before birth?
Yes. Prenatal tests called chorionic villus sampling (CVS) and amniocentesis can diagnose these diseases before birth. These tests are available when both members of a couple are carriers or when one is a carrier and the other has uncertain or unknown carrier status.
CVS generally is done between 10 and 12 weeks of pregnancy. In CVS, the doctor retrieves a sample of cells from the developing placenta either through a thin tube inserted through the vagina or by inserting a needle through the mother’s abdomen. The placenta contains cells that are genetically identical to those of the fetus, and these cells are examined for the presence of hex A (when testing for Tay-Sachs) or hex A and hex B (when testing for Sandhoff). The lab can test for gene mutations in addition to the enzyme.
Amniocentesis usually is done between 15 and 20 weeks of pregnancy. In this test, the doctor inserts a needle into the mother’s abdomen to take a sample of fluid that surrounds the fetus. The fluid contains fetal cells, which are tested for the presence of the enzyme and/or gene mutations.
Some medical centers offer genetic testing to carrier couples who undergo in vitro fertilization (a process in which eggs are removed from a woman’s ovaries and fertilized in the laboratory with her partner’s sperm). The embryos are tested for a genetic disease, and only healthy ones are implanted in the mother. This is called preimplantation genetic testing.
Couples who are carriers of a Tay-Sachs or Sandhoff gene or those who may be at increased risk due to ethnic background or family history may want to consult a genetic counselor. These health professionals help families understand what is known about the causes of a birth defect and the chances of the birth defect occurring in a pregnancy. They also help guide families through the testing process. Genetic counselors can provide referrals to medical experts and appropriate support groups in the community. Genetic counseling is available at most large medical centers and teaching hospitals. To find a genetic counselor in their area, individuals can ask their health care provider or contact the National Society of Genetic Counselors.
Does the March of Dimes support research on Tay-Sachs and Sandhoff diseases?
Yes. March of Dimes grantees helped pinpoint mutations in the hex A gene that are responsible for late-onset forms of Tay-Sachs disease. Information about specific mutations leads to improved diagnosis and carrier screening for all forms of Tay-Sachs disease.
Current grantees are attempting to develop drug treatments that may prevent the production of certain fatty substances that build up and impair brain cells in individuals with Tay-Sachs and Sandhoff diseases. This approach eventually may help prevent the loss of central nervous system function and early deaths associated with these diseases.
For more information
References
December 2009
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