"So what?" you say. Well, you have to understand that when we do research on genetics we usually don't have access to tissue since living people don't want their parts cut into. So we take a vial of blood, spin out the red blood cells which don't have DNA, and then extract DNA from the remaining leukocytes (white blood cells). Up to now it's been assumed that DNA in one cell of the body would be the same as in any other. So this puts into question any research or medical treatment that depends on genetic information from blood. Assuming the McGill University group is correct, of course.
Here's a quote from the press release:
“From a genetic perspective, therapeutic implications aside, the observation that not all cells are the same is extremely important. That’s the bottom line,” he added. “Genome-wide association studies were introduced with enormous hype several years ago, and people expected tremendous breakthroughs. They were going to draw blood samples from thousands or hundreds of thousands of individuals, and find the genes responsible for disease.
“Unfortunately, the reality of these studies has been very disappointing, and our discovery certainly could explain at least one of the reasons why.”
So much research, particularly biomedical research, involves DNA microarrays. These arrays are usually used with genetic material obtained from blood samples. If we're extrapolating from genetic samples that aren't actually representative of the subjects / patients, well, that's really bad. I'm hoping based on their not publishing in a top journal like Nature or Science that there's something hinky here.