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People who are carriers of Tay-Sachs disease can have children with the disease if the other biological parent is also a carrier. This condition causes muscle weakness, loss of motor skills, and seizures in infants. Carriers of Tay-Sachs disease do not have the disease.
More about Tay-Sachs disease
People born with Tay-Sachs disease suffer from progressive brain damage, as the condition causes cells in their brains (and spinal cords) to die. The most common form of the condition is fatal in early childhood.
There are three forms of Tay-Sachs disease:
- Infantile Tay-Sachs: This is the most common form of Tay-Sachs—and the one for which the test offered through Ancestry® tests. The infantile form typically leads to death in early childhood.
- Juvenile Tay-Sachs: This form is very rare and generally causes symptoms that start between ages 2 and 5. People with the juvenile form typically live until late childhood or their teenage years.
- Late-Onset Tay-Sachs: This form is also very rare and has symptoms that are generally milder and develop more slowly; but they can vary from person to person. Some people with the late-onset form of Tay-Sachs have shortened lifespans.
There is currently no cure for any form of the disease. But researchers are exploring various approaches to find one.
Who has Tay-Sachs disease?
Tay-Sachs is very rare: About 1 in every 320,000 babies is born with Tay-Sachs disease. And only about 1 in 250 people in the general population are carriers.
Carriers do not have Tay-Sachs. Their main issue is the risk of their children developing the disease. Each child of two parents who are carriers for Tay-Sachs has a 1 in 4 chance of being born with the disease.
While anyone can be a Tay-Sachs carrier, the condition is more common in some populations. For instance, for people of Ashkenazi Jewish descent in the U.S., the chance of being a carrier is about 1 in 30. The chances are also higher-than- typical for people of French Canadian descent, those from Old Order Amish communities in Pennsylvania, and people of Cajun descent.
What are the symptoms of Tay-Sachs disease?
Newborns with Tay-Sachs disease typically appear healthy before developing symptoms between the ages of 3 and 6 months. These symptoms include an exaggerated startle response to noises, muscle weakness, and loss of motor skills—which means they stop being able to do things like sitting, rolling over, and crawling.
Children with Tay-Sachs disease eventually develop additional symptoms such as seizures, intellectual difficulties, paralysis, and loss of eyesight and hearing. Another classic symptom of Tay-Sachs is a cherry-red spot in the eye. The most common cause of death is complications from lung infections.
Children with juvenile Tay-Sachs disease also have loss of motor control and mental function—although it typically progresses more slowly than the infantile form. They often develop infections frequently and can also experience seizures and loss of eyesight. Symptoms of juvenile Tay-Sachs disease may begin at any time during childhood, but they most commonly appear between the ages of 2 and 5. Infection is a common cause of death, often by late childhood or teenage years.
In late-onset Tay-Sachs disease, symptoms and severity can vary from person to person. And these symptoms may begin appearing anytime from adolescence to mid-30s. Symptoms can include muscle weakness, loss of coordination, difficulty speaking (or swallowing), tremors, loss of vision, and seizures. Some people also develop mental disorders such as schizophrenia. Not all people with late-onset Tay-Sachs disease have shortened lifespans, but some do.
Why is it important to learn about Tay-Sachs disease?
Currently, there is no way to cure or slow down the progression of Tay-Sachs disease. But some of the symptoms can be managed to help people with the condition be as comfortable as possible. For example, there are treatments which can help control seizures or help manage infections. And though no cure currently exists, scientists continue to research potential treatments for the condition.
Carriers of Tay-Sachs disease have no symptoms to manage because they don’t have the condition. But they could have a child with Tay-Sachs disease—if the other biological parent is also a carrier. Being a carrier of Tay-Sachs disease can affect what some couples think about when deciding to have children. Some people may do nothing with the information in partnership with their healthcare provider or genetic counselor, while others may decide not to have children. And others may, after discussing their options with a healthcare provider, choose to use a variety of techniques to lower the chances that their child will have Tay-Sachs disease.
How is Tay-Sachs disease passed down?
People who are carriers of Tay-Sachs disease most likely had it passed to them by one of their biological parents. This means that at least one of their parents is probably a carrier too.
If someone is a carrier of Tay-Sachs disease and the other biological parent is not a carrier, each child has a 1 in 2 chance of being a carrier of Tay-Sachs disease.
If both parents are carriers, each child has a:
- 2 in 4 chance of being a carrier of Tay-Sachs disease
- 1 in 4 chance of having Tay-Sachs disease
The fact that a child of two carriers of Tay-Sachs disease has a 1 in 4 chance of having the condition is what’s most concerning for many carriers.
Here is how the inheritance works in most cases: A person has two copies of most of their genes, one from each parent. To have Tay-Sachs disease, they would need two DNA differences linked to Tay-Sachs disease—one in each copy of the gene tied to the disease. If someone only had a DNA difference in one copy of this gene, they would be a carrier. This is called autosomal recessive inheritance.
What causes Tay-Sachs disease and what does the test offered through AncestryHealth® look at?
Tay-Sachs disease is caused by DNA differences in the HEXA gene, which helps break down a type of fatty acid in the brain. People have two copies of this gene. In people who have a DNA difference in both copies, the fatty acid doesn’t get broken down as well, which causes serious damage to the brain and spinal cord.
The test offered through AncestryHealth® looks for specific DNA changes in the HEXA gene. This is the only gene known to be associated with this condition. AncestryHealth®, powered by next-generation sequencing, can detect over 90% of the known DNA differences linked to carriers of Tay-Sachs disease.
What does this gene do? The HEXA gene helps make something found in all human cells called beta-hexosaminidase A. It is important for making sure people’s cells can remove toxins. When it isn’t working, these toxins build up. In Tay-Sachs disease, a certain toxic substance builds up in the brain and causes progressive damage.
AncestryHealth® includes laboratory tests developed and performed by an independent CLIA-certified laboratory partner, and with oversight from an independent clinician network of board-certified physicians and genetic counselors. The test results are not diagnostic and do not determine your overall chance of developing a disease or health condition. The tests are not cleared or approved by the U.S. Food and Drug Administration. You should consult a healthcare provider before taking any action based on AncestryHealth® reports, including before making any treatment, dietary, or lifestyle changes. AncestryHealth® is not currently available in New York, New Jersey or Rhode Island.
- Genetics Home Reference. Tay-Sachs Disease. Accessed July, 2019. www.ghr.nlm.nih.gov/condition/tay-sachs-disease#
- Kaback MM, Desnick RJ. Hexosaminidase A Deficiency. 1999 Mar 11 [Updated 2011 Aug 11]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2019. Available from: www.ncbi.nlm.nih.gov/books/NBK1218/
- National Organization for Rare Disorders. Tay-Sachs Disease. Accessed July, 2019. www.rarediseases.org/rare-diseases/tay-sachs-disease/