Recent advances in genetic testing: how does it work?

Posted 6 years ago by Andreas Obermair

Last year, my practice started offering genetic testing to patients in partnership with a US-based genetic testing company. Genetic tests can now be started online by the doctor. Then, the patient will complete the order from home. It cost $US 249.

It requires 3 mL of sputum (saliva), which is posted to the United States. Your doctor can track the status of the sample. Both the patient and your doctor will be notified when test results are available by email. I then can log into the secure platform and download the results to discuss with the patient in person.

The key features of this new test are:

• The test measures not only BRCA1/2 or Lynch but checks on 30 hereditary (genetic) mutations;
• Patients do not need to wait for an appointment to have genetic testing;
• All patients are eligible (patients for genetic testing in other institutions need to meet certain eligibility criteria that may change from time to time);
• Patients do not need to have a blood test;
• Test results are available promptly.

Before I order a genetic test, it is important to understand the implications of genetic testing and we always discuss them in a proper consultation before patients have the test. I supervise the process through to delivery of the results.

Genetic testing is not for everybody. In my previous blog I discuss if patients would rather not know if you have an inherited, increased risk of cancer.

A few important points to remember:

1. A negative result does not mean there is guaranteed no genetic fault. It simply means that there is no mutation in one of the 30 genes that were tested. Gene defects that are not yet discovered cannot be diagnosed.

2. A positive test result should be followed by a confirmatory (blood) test.

3. A positive test has implications not only for the patient but for all first-degree relatives (siblings, children). Conversations about genetic faults can enhance family relationships but it can also cause a strain on those. It is up to the patient to determine what family members wish to be informed about a genetic test result and who prefers to remain in the unknown.

A recent study from Belfast re-tested 500 women who tested negative for BRCA 1/2 previously. These women had a strong family history of breast and ovarian cancer. At re-testing a significant number of women tested positive for a mutation other than BRCA.

In my experience, all patients that I offered genetic testing were keen to know their genetic risk factors and appreciated the value of the information.

Case Example using the new testing:

Mrs X.Y., 55 years, requested genetic testing. She has a strong family history of breast cancer and requested a prophylactic hysterectomy, BSO, regardless of the gene test. The saliva gene test confirmed that she is negative for BRCA. But the test also revealed she has a mutation in one of the other genes associated with breast and pancreatic cancer. While she is negative for BRCA, she carries another less known mutation.

Also, her first-degree relatives (siblings, children) require genetic testing (available for only $50) because they have a 50% chance of also carrying this genetic mutation. Would this patient have had a “normal” BRCA blood test, she would have been told that she is BRCA negative and she would have nothing to be concerned about. The new test achieved a much better result for her.

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