Tay-Sachs disease

Diagnosis and Testing

How do I get tested for Tay-Sachs disease?

Some people may get screened for Tay-Sachs disease if they are in a group or population that has an increased risk of having the disorder, such as being of Ashkenazi Jewish descent. Screening may involve a blood test to assess the activity of the enzyme hexosaminidase A. This enzyme is deficient in people with this disorder, and absent or nearly absent in infants with infantile form (the most common form). This enzyme can be measured through a simple blood test. The blood sample must be sent off to a laboratory that specializes in testing for Tay-Sachs disease.

Molecular genetic testing can also be used to screen for Tay-Sachs disease. These tests involve studying the HEXA gene for changes that cause the disorder. This can include sequence analysis, where a part or sequence of DNA within a gene is examined, or gene-targeted deletion/duplication analysis, where missing or extra regions of DNA are looked for within a specific gene. Molecular genetic testing must be done at specialized laboratories.

In families with no history or known risk of Tay-Sachs disease, the diagnosis is made by a physician. Sometimes a referral to a metabolic or genetic disease specialist is required before a diagnosis is made. A doctor may suspect Tay-Sachs disease because of specific symptoms such as a cherry red spot in the eyes, increased startle response, loss of previous acquired skills, muscle weakness, decreased attentiveness, and other common symptoms. The screening tests described above can be used to confirm a diagnosis of Tay-Sachs disease in affected children.

To find a medical professional nearby who can discuss information and testing, a listing of medical geneticists can be found at the American College of Medical Geneticists website and genetic counselors can be found on the National Society of Genetic Counselors website.

References
  • Kaback MM, Desnick RJ. Hexosaminidase A Deficiency. GeneReviews website. Accessed September 20, 2016. http://www.ncbi.nlm.nih.gov/books/NBK1218/
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More Diagnosis and Testing Content

Is there newborn screening for Tay-Sachs disease?

What tests support a diagnosis of Tay-Sachs disease?

Who else in my family should I test for Tay-Sachs disease?

Can Tay-Sachs disease be detected before birth?

Is there newborn screening for Tay-Sachs disease?

Tay-Sachs disease is not available on newborn screening as of September 2016. However, if there is a family history of Tach-Sachs disease or a doctor has reason to suspect a child may have the disorder, testing can be done on babies at or shortly after birth.

If a baby appears to have health problems that could be caused by Tay-Sachs disease, the easiest way to begin testing for the disorder is to discuss it with the pediatrician or primary doctor. Referral to a metabolic genetic specialist may be necessary. Testing information in your area can also be obtained through a genetic counselor, to find a genetic counselor visit the National Society of Genetic Counselors Find a Genetic Counselor website. Information on how to add a disorder to newborn screening programs can be found at Save Babies Through Screening Foundation.

References
  • Save Babies Through Screening Foundation website. http://savebabies.org/
What tests support a diagnosis of Tay-Sachs disease?

There are different tests that can be used to diagnose Tay-Sachs disease. An enzyme assay is standard for diagnosing this disorder. An enzyme assay is a test that measures the activity of an enzyme. Doctors take a blood sample and send it off to a lab where they measure the sample for hexosaminidase A activity. If this enzyme is low or absent, that means a person has Tay-Sachs disease.

Molecular genetic testing can also be used to confirm a diagnosis. These tests involve studying the HEXA gene for changes that cause the disorder. This can include sequence analysis, where a part or sequence of DNA within a gene is examined, or targeted mutation analysis, where the six most common mutations in the HEXA gene that cause Tay-Sachs disease are searched for, or deletion/duplication analysis, where missing or extra regions of DNA are looked for within a specific gene. Molecular genetic testing must be done at specialized laboratories.

There are more tests a doctor might perform when assessing someone for Tay-Sachs disease. These may be done to detect or assess specific symptoms. For example, an eye exam may reveal cherry red spots on the retina.

Talk to your doctor about what the results of these tests may mean in Tay-Sachs disease. To find a genetic medical professional nearby who can discuss information and testing, a listing of medical geneticists can be found at the American College of Medical Geneticists website and genetic counselors can be found on the National Society of Genetic Counselors website.

References
  • Kaback MM, Desnick RJ. Hexosaminidase A Deficiency. GeneReviews website. Accessed September 20, 2016. http://www.ncbi.nlm.nih.gov/books/NBK1218/
Who else in my family should I test for Tay-Sachs disease?

In a family with Tay-Sachs disease, tests can be done to see whether other family members are carriers for the disorder. (Carriers do not have symptoms and have one working and one non-working copy of the HEXA gene.) However, the specific gene changes in that family needs to be known. If known, all siblings and other at-risk relatives can be tested. Molecular genetic testing, which are tests that look for changes to genes, can be performed. A newborn child in a family with a history of Tay-Sachs disease should be tested through molecular genetic testing. An enzyme assay, which is a test that can measure the activity of the hexosaminidase A enzyme in certain cells, can also be used to test at-risk family members). A genetic counselor or a physician with experience in Tay-Sachs disease can provide advice about how a confirmed diagnosis can affect other family members. Medical geneticists can be found through the American College of Medical Geneticists and a genetic counselor can be found through the National Society of Genetic Counselors.

References
  • Kaback MM, Desnick RJ. Hexosaminidase A Deficiency. GeneReviews website. Accessed September 20, 2016. http://www.ncbi.nlm.nih.gov/books/NBK1218/
  • Tay-Sachs Disease. The National Organization for Rare Disorders website. Accessed September 20, 2016. http://rarediseases.org/rare-diseases/tay-sachs-disease/
Can Tay-Sachs disease be detected before birth?

Some parents may choose to have their children tested for Tay-Sachs disease before they are born. This is known as prenatal diagnosis. A sample of tissue can be taken from the placenta to test for the activity of hexosaminidase A activity or for changes in the HEXA gene. This test is called chorionic villus sampling. Another test is called amniocentesis, which involves taking a sample of the amniotic fluid that surrounds and protects a developing fetus. Cells known as amniocytes are taken from the fluid and studied for the activity of hexosaminidase A activity or changes in the HEXA gene. There are risks to the unborn baby of doing these tests before birth. The gene change(s) that causes Tay-Sachs disease must be known in a family to do molecular genetic testing (which can detect these changes). Talk to your doctor or a genetic counselor in your area to discuss the risks and benefits of prenatal diagnosis.

References
  • Kaback MM, Desnick RJ. Hexosaminidase A Deficiency. GeneReviews website. Accessed September 20, 2016. http://www.ncbi.nlm.nih.gov/books/NBK1218/
  • Tay-Sachs Disease. The National Organization for Rare Disorders website. Accessed September 20, 2016. http://rarediseases.org/rare-diseases/tay-sachs-disease/

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