is performed to identify individuals who have a gene mutation
and may be at risk for having a child or other family members with the same mutation. Carriers
usually do not have symptoms related to the gene mutation. Carrier testing is typically offered to individuals who have family members with a genetic condition, family members of an identified carrier, and individuals in ethnic or racial groups known to have a higher carrier rate for a particular condition.
There two types of carrier screening
and biochemical. Sandhoff carrier screening is available through DNA or biochemical testing. DNA carrier screening detects specific known mutations that are ‘looked’ for in the test. A negative DNA carrier result does not eliminate an individual's chances of being a carrier because of the possibility of carrying an unknown mutation or one not ‘looked’ for in the test. Biochemical testing, also called an enzyme
assay, detects the level of the enzyme(s) in question in the blood. Enzyme assays can be done using serum
(white blood cells
). Serum is typically the standard test, but leukocyte testing is recommended when the person being tested is pregnant, on birth control pills or taking any medications that affect hormones
because all of these situations can potentially interfere with the accuracy of the serum test. DNA carrier screening may be recommended if the results of the biochemical test are uncertain.
Sandhoff disease is associated with deficiencies of both hexosaminidase A (hex A) and hexosaminidase B (hex B) enzyme activity. Carriers of Sandhoff disease have reduced (but adequate) amounts of both hex A and hex B. While most hex A assays are performed to identify Tay-Sachs carriers, the test also can also identify individuals that are carriers of Sandhoff disease. Looking at the total hexosaminidase activity in combination with the percent of hex A activity present can aid in determining whether an individual is a carrier of Sandhoff disease. Typically, a decreased amount of total hexosaminidase activity along with an increase in the proportion of hex A activity in leukocytes is suggestive of a Sandhoff carrier.
In contrast, Tay-Sachs carriers have a decrease in the amount of hex A activity. When the hex A enzyme result indicates that an individual is a possible Sandhoff carrier, the next step is typically to offer carrier testing to the individual's partner. If the partner is negative, the risk for the couple to have a child affected with the disorder is very significantly decreased. If the partner is also a possible carrier, more comprehensive testing may be offered.
We are unable to make recommendations about genetic screening
and/or testing, but we do recommend genetic counseling
for questions about carrier and prenatal genetic screening. Genetic counselors
are non-directive healthcare professionals that help individuals understand their options. Genetic counselors are very knowledgable about testing guidelines and procedures. They can help a person to understand the tests and what the results mean for individuals, partners, children and extended family members.
Last updated: 8/22/2011
is unique because the results also provide information about risks for family members. For this reason, individuals are often encouraged to consider sharing genetic test results with relatives. Genetic test results can have a significant medical and emotional impact on the person who had the test, as well as on their family. When a person tests positive on a genetic test for a specific condition, their children, siblings, parents and other extended family members may have a chance of also testing positive.
Genetic test results can help people make informed decisions about managing their health care. A positive result can direct a person toward available prevention, monitoring, and treatment options, depending on the condition involved. Some test results can also help people make decisions about pregnancy and having children.
If you decide to share your genetic test results with other family members, it is often helpful to provide relatives with a copy of the test report. Relatives can talk with their doctor or meet with a genetic counselor to discuss their risk for the genetic condition. A genetic counselor can discuss the risks, benefits, and limitations of genetic testing.
Last updated: 8/29/2011
Last updated: 7/15/2016