Male DNA Commonly Found in Women’s Brains | Hacker News Reader

Male DNA Commonly Found in Women’s Brains

sciencedaily.com

35 pointsdaegloe8 comments

This story already made the rounds on wednesday http://news.ycombinator.com/item?id=4582655

I'm yet to read the paper, but the comment highlighted in the thread from Wednesday raises some points[1]. For ease of access I'll re-replicate it here;

"This is just a PCR study. No evidence that the foreign human DNA even entered host cells, much less that it was expressed. Probably shows only that minute quantities of foreign human DNA can hang around a host body for a while. Most likely explanation is that it gets bound up in the extracellular matrix. Being that the DNA is of human origin, it would not trigger an immune response, but rather, it would just be slowly degraded like the host's own DNA when it is released from dead cells (part of the normal, perpetual turnover of cells). DNA is hardy stuff; people have sequenced DNA from Neanderthal bones. Study co-author J. Lee Nelson's comments are ridiculous hype. He should be ashamed of himself. That those comments were published in this newspaper uncritically is also an embarrassment. This work was published in PLoS ONE. PLoS ONE articles are peer reviewed only for the validity of the methods used, not for the importance of the subject matter or the validity of the conclusions drawn. This is where you can publish all sorts of meaningless crap."

I disagree with the extremity of the commentor's view on PLoS ONE articles, and feel they should perhaps have noticed that Dr. Nelson is a lady, not a dude, but still something worth considering.

[1] - http://www.latimes.com/health/boostershots/la-heb-women-brai... , comment 2

Original paper has also been posted here, for those interested.

http://news.ycombinator.com/item?id=4582700

Male Microchimerism in the Human Female Brain

Considering that everyone of us, without exception, gets 50% of our DNA from our father, the phrase "male DNA" deserves some definition. One assumes that perhaps they are talking about DNA that is normally only found on the g Y-chromosome, but they don't say that, and in this case, that is an unfortunate oversight. A science publication should not leave readers guessing about what exactly is being discussed.

They do use the phrase "male cells of fetal origin" but they don't explain why these are male cells. There are several possible explanations, and I am curious which one is true here. Again, they could be talking about a type of expression that relates to Y chromosome. But there was last year the interesting study that suggested end-stage cells know their sex through a process we do not yet fully understand. So what is this study actually saying? I wish they had clarified what "male DNA" means in this context.

It may simply be that testing for maleness is the easiest way to prove that the cells are of "foreign" origin.

At the bottom of the article, there is a link to the original paper:

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna...

...which can be downloaded (i.e. not behind a pay-wall). From the abstract:

"In this study, we quantified male DNA in the human female brain as a marker for microchimerism of fetal origin (i.e. acquisition of male DNA by a woman while bearing a male fetus). Targeting the Y-chromosome-specific DYS14 gene, we performed real-time quantitative PCR in autopsied brain from women without clinical or pathologic evidence of neurologic disease (n = 26), or women who had Alzheimer’s disease (n = 33). We report that 63% of the females (37 of 59) tested harbored male microchimerism in the brain."

The cells are presumed to have migrated into the women from a male fetus previously carried (perhaps not to term) by the subjects, as indicated by the 1st paragraph definition of microchimerism ("the harboring of genetic material and cells that were exchanged between fetus and mother during pregnancy") and the start of the 3rd paragraph:

Chan said the study is the first description of male microchimerism in the female human brain. The findings support the likelihood that fetal cells frequently cross the human blood-brain barrier and that microchimerism in the brain is relatively common. Until this study, it was not known whether these cells could cross the barrier in humans.

I think it's only the strong proof that such cells reach and persist in the mother's brain that's new about this study; that persistent cells are exchanged in both directions between mother and fetus has been known for a while. See for example this 2005 NYTimes story:

http://www.nytimes.com/2005/05/10/health/10bloo.html?pagewan...

Another route to chimerism is through the cells that routinely pass from a mother to fetus and remain there for life.

Dr. Ann Reed, chairwoman of rheumatology research at the Mayo Clinic, who uses sensitive DNA tests to look for chimerism, finds that about 50 to 70 percent of healthy people are chimeras. The more scientists look for chimerism, the more they find it.

The most famous cases are those where a child turns out to match a (possibly 'vanished' while in womb) 'aunt' moreso than the birth mother. But I suspect at some point there will be a proven case where a child is found to be, genetically, the direct offspring of their matarnal grandmother's primary genome -- if the mother's egg cell was descended from a persistent grandmother cell rather than the usual mixed maternal-grandfather/matrernal-grandmother cell. (Or even in suitably rare situations, great-grandmother, etc.)