My genetic test was negative, so I'm not at risk of getting the disease for which I’ve been tested
It's a myth!
It’s estimated that humans have 20,000 different genes, and so far we can offer clinical genetic testing for about 6,000 of them; therefore, it is not possible to test all genetic possibilities. In addition, several genes can be associated with the same disease; for Parkinson’s disease, for example, a dozen genes are currently known.
If you get a negative genetic assay result, this means that no mutation (preventing the gene from functioning normally) has been identified among the genes tested. It can therefore be concluded from this test that your risk of developing a disease associated with these genes is significantly reduced.
Why “significantly reduced” and not “totally nil”? Because this result does not completely exclude the possibility of a hereditary disease or predisposition. Indeed, it is possible that the person being tested may be a carrier of a:
Mutation that is currently unknown in one of the genes tested;
Mutation in a gene that has not been tested;
Mutation in a gene that is still unknown.
Furthermore, certain diseases can be associated with both genetics and other factors, as is the case for cancer: a woman whose genetic test (for the BRCA gene, for example) is negative has no increased risk of developing breast cancer, but still remains at risk, at the same percentage rate as the general population.
It is also important to note that not all genetic tests are equal: they must be undertaken using the right technology, the right laboratory, what genes are to be tested, etc. There is also the fact that certain laboratories offer incomplete analyses: a “negative” result (no mutation identified) can in fact be a false negative. To help you make an informed decision when selecting a genetic test, it is best to discuss it with an expert.