What does the TCF7L2 test look for?
The TCF7L2 test is designed to look for a specific genetic variant. This one-letter variation has been shown to be associated with an increased risk of type 2 diabetes in large studies across the world. In 2006, scientists at deCODE Genetics discovered that individuals who have two copies of this one-letter variation in the TCF7L2 gene have around twice the risk of having type 2 diabetes compared to those who have one or no copies of the risk variant. About 18% (1 in 5) of people with diabetes carry two copies of this variant compared to about 8 to 11% (1 in 10) of the general population.
What does a positive result mean?
A positive result means that you carry two copies of the risk marker and thus, are at increased risk for diabetes. Clinical studies show that people with positive test results have around twice the risk for developing diabetes as the average person. This increased genetic risk is independent of the impact of other risk factors, such as obesity, diet, and exercise. Together, your genes plus your lifestyle and family history provide a more complete picture of your risk for diabetes.
A positive result does not mean that you will definitely develop diabetes. There are many factors that affect the development of diabetes and the TCF7L2 risk marker is just one of them.
What does a negative result mean?
Negative results mean one of two things: you have no copies of the risk marker, or you have one copy of the risk marker. Clinical studies show that people without the risk marker have the same risks for diabetes as the average person. The same studies also show that people who have just one copy of the risk marker do not have a medically significant increased risk for developing diabetes compared to the average person.
What if my doctor hasn't heard of this test?
The TCF7L2 test is a new test and was just released to the medical community in April 2007. Although the body of research surrounding this risk marker is very large, the research was conducted very recently, so not all doctors may be familiar with this genetic marker.
Will insurance pay for my test?
The company and laboratory that developed the TCF7L2 test is currently negotiating with insurance companies for reimbursement coverage. Until coverage is achieved, it is likely that you will need to cover the cost of the test.
Is the TCF7L2 test FDA-approved?
This test was developed and is performed by the deCODE Genetics Reference Laboratory, which is a CLIA-certified laboratory. CLIA stands for the Clinical Laboratory Improvement Amendments. All laboratory testing (except research) on humans is regulated by The Centers for Medicare & Medicaid Services through CLIA. The TCF7L2 test is not required to go through FDA review and, like most genetic tests, it has not been cleared or approved by the FDA.
How much do other diabetes risk factors — obesity, family history, and so forth — increase my risk?
While it is not possible to come up with a specific number for these combined risks, the important thing to remember is that diabetes risk factors add up. This means that someone who has many risk factors has a greater chance of developing diabetes than someone with only one risk factor.
Reviewed by Francine Kaufman, MD. 4/08
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