DNA Differences Observed Between Blood and Organs

Scrameustache writes "Researcher working on a rare type of aortic abnormality found that the DNA from diseased tissue did not match the DNA from the blood of the same patients So far it's unclear whether these differences in the blood and aortic tissue are the consequence of RNA editing, which changes the messenger RNA but not the gene, or DNA editing, which involves differences in the gene itself. Based on the evidence so far, the researchers believe the differences resulted from developmental rather than somatic DNA alterations. 'Traditionally when we have looked for genetic risk factors for, say, heart disease, we have assumed that the blood will tell us what's happening in the tissue,' lead author Bruce Gottlieb said in a statement. 'It now seems this is simply not the case.'"

Chimera

[John Hasler]

Perhaps some of those patients were chimeras [wikipedia.org].

Re:complexity

[jeffliott]

Unfortunately, yes, if there is nothing magical about the chemistry that occurs in our bodies. This is unfortunate because at some point, we will stop being interesting to look at. However, the idea of a disease free world is probably well worth it, and we shouldn't be discouraged to keep trying to figure this stuff out simply because it is getting harder.

I'm curious and not a Biologist-

[mckinnsb]

... but would this discovery have any potential legal ramifications on DNA testing, potentially casting doubt on its validity? Their testing method has to be accurate, or else they could not observe the differences in DNA between blood and organ cells - but are the differences enough to cause one person's DNA to be mistaken for another, or are they small enough to not risk a false positive? I'm not a lawyer or a biologist, but thats the first thing that popped into my head.

Re:good old days

[designlabz]

Well, i guess, medicine is what happened. In the "good old days" if you were seriously messed up on birth, you would simply die. But now days, doctors can patch you up, so you give birth to more messed up humasn, that will then breed with healthy humans, and eventually create a race where no one is really healthy. That is called backward evolution and is nicely described in Idiocracy ( http://www.imdb.com/title/tt0387808/ [imdb.com] ). Some people would call it inhuman or sick, but in my humble opinion medicine should be limited to fixing injuries and curing viruses and infections, rather than helping non-adapted survive. Life is a game of numbers. Not everyone is meant to win. Just look at complexity of our bodies... there is so many things that can and often do go wrong. Call it God or Evolution... each and every one of us is an experiment... and not all experiments lead to a great discovery... in fact, most of them fail. But, in a world governed by emotions, empathy and cash no one ever cares about real progress. Bottom line: When we started cheating in a game of life, we gave up on evolution. That was the moment we stopped being a specie and started being... a goo?

Re:I'm curious and not a Biologist-

[turtledawn]

Typically one would compare DNA collected via the same method as the original specimen- thus if you were testing for DNA in a skin flake, you would get a skin sample, while for semen, you'd get a semen sample, etc. It shouldn't make a difference in a well-run criminal case (and I'm not going to touch whether or not DNA-reliant cases are well run).

House episode?

[Anonymous Coward]

Wasn't there a House M.D. episode covering something just like this where the organs and the blood DNA didn't match?

Re: Mosaic

[nbauman]

Actually TFA did raise the possibility of chimeras. My thought was that it could be a mosaic http://en.wikipedia.org/wiki/Mosaic_(genetics) [wikipedia.org]

People sometimes get mosaicism after stem cell transplants or organ transplants.

I saw an interesting example of mosaicism in a medical journal. An infant was born with half male genitals, half female genitals. The most obvious explanation was that he/she was born of two embryos, one male, the other female, that combined at an early stage (but not too early) and formed a mosaic individual, with patches of male and female cells. Mosaicism actually is pretty common in biology. Sometimes you get patches of skin that vary between 2 colors. The later the embryo recombines, the bigger the patches are.

But this raises the possibility that the DNA of the cells in one developmental branch -- the arteries, or the aorta -- goes through some epigenetic doubling, on a routine basis, because it happened in several samples, even healthy tissue. I wonder if it happens in mice.

My understanding of the article was that they sequenced DNA -- both strands -- not the RNA. But for reasons I don't understand, Schweitzer said it might be the consequences of RNA editing, to the messenger RNA.

Actually they got into chimerizaton at the end of TFA:

In an e-mail message to GenomeWeb Daily News, Navigenics Co-founder and Chief Science Officer Dietrich Stephan said the team's work is interesting and deserves further investigation.

"Differences between the germ-line genome and somatic cells is well established in cancer. It is also well described that chimeras can result from early DNA changes in early embryonic development that propagate to form regional differences in the genome across the body," Stephan noted.

Small Scale Evolution?

[NoMoreFood]

I am not a doctor nor did I completely follow the article, but I assume the cell lifetimes differ between blood and organ tissues. Given this, would we not expect some some sort of micro-evolution going on in frequently-reproducing cell types?

Re:Small Scale Evolution?

[Tacvek]

I do know that a form of micro-evolution is how the body produces antibodies. The antibody producing cells attempt to produce mutations in the antibody gene. Some form of regulatory system promotes the cells that produce the antibodies that best bind to the pathogen, and destroys others. Eventually antibodies that bind really well to the pathogen will result.

I'm sure that is is simplified explanation, but that is roughly what I was taught in biochemistry.

But I don't think mutations otherwise occur at high enough a rate in other cases for micro-evolution to occur.