A group of researchers from McGill University studying abdominal aortic aneurysms published a paper in the July issue of Human Mutation that has serious implications for all large scale genetics studies that have been started in the last 15 years (except for those using DNA from cancer cells), including those funded by the National Human Genome Research Institute and studies that are the basis for new gene therapies and genetic testing.
The group of researchers found that contrary to what had been previously thought, the DNA in every cell in a person's body is not essentially identical. This is huge because genetic tests for diseases have traditionally used DNA from the blood in order to test a person for risk of a given disease (with many consumer genetic tests using saliva). The fact that one cannot just use any DNA found in the blood or saliva, but must instead extract DNA straight from the problem cells, means that all previous genetic studies, aside from those that used cancer DNA, will need to be redone and all future studies cannot rely on just blood samples from people. Not to mention that in order to perform genetic studies and tests, doctors will need to be able to get sample cells directly from the person's tissues that they are worried about.