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Tuesday, October 21, 2014

Male DNA in Female Brains? Yes!

Posted by jlwile on January 9, 2013

Male DNA was found in 63% of the women studied.
(Public domain image)

A gene called DYS14 is found only on the Y chromosome in human beings. Of course, only males have a Y chromosome, so it is reasonable to assume that the only place you will ever find this gene is in men, right? Wrong! William F. N. Chan and his colleagues examined the brains of 59 deceased women, and they found the gene residing in 37 of the brains studied! In other words, 63% of the deceased women studied had male DNA in their brains. Interestingly enough, in most of those brains, the DNA was found in several different places!1

How in the world did male DNA get into these women’s brains? The researchers aren’t sure, because they don’t have detailed medical histories for most of the women. However, the most likely explanation is that the DNA comes from the male children that these women carried. I have written about this phenomenon, called fetomaternal microchimerism, before. As I mentioned in that article, when I first heard about a baby leaving cellular remains inside his or her mother, I thought it couldn’t possibly be true. However, I was wrong. There is solid evidence to suggest that not only do babies leave a lasting, cellular imprint on their mothers, mothers do the same for their babies.

However, the possibility that children leave some of their DNA behind in their mother’s brain is very surprising. After all, the cells that make up the brain are incredibly sensitive. In fact, the contents of your own blood are toxic to your brain cells. As a result, you have an elaborately designed blood-brain barrier that shields your brain cells from your blood. This barrier is so vigilant that it allows only certain substances (such as the glucose and electrolytes that the brain cells need) to pass through it. As a result, your brain cells are protected from the majority of substances found in your bloodstream.2

Of course, the blood-brain barrier is not perfect. It allows some substances that aren’t good for your brain cells to pass through it as well. Ethyl alcohol can pass through the blood-brain barrier, for example. That’s why your thinking is impaired when you drink too many alcoholic beverages. Many illicit drugs can also pass through the blood-brain barrier, which is why they produce a “high.” In fact, the potency of a mind-altering drug is partly due to how well it passes through the blood-brain barrier. For example, heroin is chemically very similar to morphine. However, because of the details of its molecular structure, it passes through the blood-brain barrier more easily than morphine. As a result, heroin’s potency as a mind-altering drug is higher than that of morphine.3

Well, the authors note that the blood-brain barrier does change during pregnancy, altering slightly what can and cannot pass through it. Thus, they suggest that when a mother carries a child, some of its cells (or at least some of its DNA) pass through the altered blood-brain barrier and take up residence in the brain. What do they do when they are there? No one is sure. Indeed, the authors note:

At present, the biological significance of harboring Mc in the human brain requires further investigation. Mc appears to persist in the blood, bone, and bone marrow for decades and is present among different hematopoietic lineages. Moreover, Mc appears to integrate and generate specific cell types in tissues. (Note: The authors use “Mc” to abbreviate microchimerism)

So while we know that babies leave traces of themselves behind in their mother, it’s not clear exactly what those traces do. Nevertheless, this study provides a tantalizing possibility. As I noted in my previous post about fetomaternal microchimerism, there are some who think that the cells of a baby in his or her mother target damaged tissue and help to repair it. While there is some evidence for this idea, it remains very controversial. However, this particular study provides a tiny amount of evidence to support that idea.

The authors note that 33 of the deceased women in their study had Alzheimer’s disease. They found that these women had a lower prevalence of male DNA in the brain and lower concentrations of that DNA in regions that are most affected by Alzheimer’s disease. The authors are quick to note, however, that their sample size is very small, so it is possible that this correlation is nothing more than a statistical anomaly. However, if it is confirmed in other, more statistically-significant studies, it suggests that the remains a child leaves behind in his or her mother’s brain might be fighting against neurological disorders like Alzheimer’s disease!

Regardless of whether or not that’s true, these results and others strongly suggest that babies leave traces of themselves throughout their mother, including in their mother’s brain. Further studies on this very interesting phenomenon will hopefully tell us more about why this is the case.

REFERENCES

1. William F. N. Chan, Cécile Gurnot, Thomas J. Montine, Joshua A. Sonnen, Katherine A. Guthrie, and J. Lee Nelson, “Male Microchimerism in the Human Female Brain,” PLoS ONE 7(9):e45592 doi:10.1371/journal.pone.0045592, 2012
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2. Gerard J. Tortora and Sandra Reynolds Grabowski, Principles of Anatomy and Physiology, 10th Edition, John Wiley and Sons, Inc. 2003, p. 452
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3. Paul M. Gahlinger, Illegal Drugs: A Complete Guide to Their History, Chemistry, Use and Abuse, Plume 2004, p. 132
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Comments

6 Responses to “Male DNA in Female Brains? Yes!”
  1. Seth says:

    I wonder if, of the 63% woman that the Y gene was found, how many of them gave birth to boys?

    Could the other 37% of woman not have had any connection with a male baby?

  2. jlwile says:

    The researchers didn’t have medical records, Seth, so they cannot determine how many of the women with male DNA in their brains gave birth to boys. However, as they point out in their article, there are other ways that women could get male DNA in their brains without actually giving birth to a boy. For example, if a mother was pregnant with a boy but it ended in a miscarriage, the pregnancy process could be enough. Also, there is a process that occurs in twin pregnancies where, early in the pregnancy, one twin absorbs the other. In the case of fraternal twins, the twins can be of different genders. Thus, the girl twin could absorb the boy twin, which might lead to male DNA in her brain. However, such rare events would not explain why the majority of the women had male DNA in their brains.

    As for the ones who didn’t have male DNA in their brains, remember that it’s not a connection with a male baby that’s important. It’s being pregnant with a male baby. It would not surprise me that roughly 1/3 of women either have never been pregnant or have never been pregnant with a boy. Once again, of course, there is no way to be sure, since complete medical records were not available.

  3. Juana Mikels says:

    Hi Dr. Wile! This blog post was mighty interesting. I actually don’t have a comment on it, except to say what a wonderful science discussion it makes. Science is never meant to be boring.
    I wanted to know if I could email you a question about my daughter (born totally blind), & your science materials. She begins high school next year. Science in public school for her has been so terribly boring & not taught in a way for her to have her mind engaged. (& she has quite a mind!) The local high school told me I could homeschool her for science & asked if it was online. So sorry to interrupt your readers train of thought, didn’t know other way to leave you a message.

  4. jlwile says:

    Thanks for your comment, Juana. I will send you an E-MAIL.

  5. Green Jean says:

    This is fascinating stuff. If your hypothesis is correct about MC protecting or repairing damaged tissue, I would think that women who had more children would have a lower incidence of degenerative diseases like Alzheimer’s. That would be an easier study to do than analyzing brains since you could just ask questions–How many children do you have? What diseases do you have?
    Do you know of anyone doing a study like this?

  6. jlwile says:

    Green Jean, I agree that your proposed study would be easier, but I wouldn’t think it would be very conclusive. There are lots of factors involved in disease. For example, stress can increase the likelihood of certain diseases, as can the previous infectious diseases you have contracted. While having kids might reduce the risk of some diseases due to Mc tissue repair (if that hypothesis is correct), having kids can also increase stress, increase the likelihood of you contracting infectious diseases, etc. Thus, it’s not clear what a study like that could conclude.

    Now…having said all that, there are some studies similar to the one you suggest. For example, the Women’s Health Study started “in 1993 to test the benefits and risks of low-dose aspirin and vitamin E in the primary prevention of cardiovascular disease and cancer in U.S. women.” However, it is still going on today, with the women filling out questionnaires about their current health. They might, indeed, have information regarding number of children, etc., so it might be possible to do what you suggest with existing data.

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