Just not the Same

There's an interesting press release from McGill University today. Apparently some of their researchers (Dr. Morris Schweitzer, Dr. Bruce Gottlieb, Dr. Lorraine Chalifour and colleagues) have a paper coming out in the journal Human Mutation today which suggests that the DNA in white blood cells isn't the same as that of normal tissue.

"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.


srp said…
I would have thought that the success of transplants even with the immune suppression drugs, would have been really impacted by this, if it were true. Of course, if we find that this is true... then, what's to say that every different type of tissue and organ in one person doesn't have different DNA. I just don't see how that could be.

Not accounting for possible mutations... each person starts as a single cell. NO, I don't think we should throw out everything over this one, quite questionable study.
kenju said…
That just sounds weird. I don't see how it could be.
Teresa said…
With all the CSI shows and how there's almost always some DNA testing on blood, it's been bothering me... what happens to the DNA in transfused blood? I'm assuming it must be rejected by the recipient and fairly easily separated and eliminated... otherwise, there'd be host-donor rejections (and presumably death) or anyone who recieved my blood donations could leave my DNA around (and that'd be a NIGHTMARE!). Hmmmm...

But this article... while I'm not a biologist, it seems that the premise would be that all cells aren't created equal. Isn't that why we have different features and grow differently, even within our own bodies? Why wouldn't blood have differences in cells?

But I do think that this study is overthinking something as I thought that most genetic testing was done with a blood test (though I know some is done with bone marrow...), and yields results...
utenzi said…
When you get blood it's usually either plasma---no cells---or packed red blood cells, which have no nuclei and thus no DNA. One reason for assuming all DNA in cells is equal is that we start off as one cell. Assuming the cells duplicate accurately each resulting set of cells should have the same DNA.
srp said…
Yes, red cells have the nucleus extruded in the marrow before going into the blood stream... usually. Of course testing of donor blood would show if any nucleated red cells were present and they would not use that blood.. would also see that the donor was checked out by their physician... as this is only a normal finding in bird blood. But yes... no DNA in red cells... white cells, yes... red cells no. The white cell DNA degenerates with the cell... white cells don't live long in a transfused state.. usually go to the place they are needed to ward off infection and then die. Good question though.

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