Mom gets DNA from you in ‘reverse inheritance’

We inherit our distinct physical form from our parents, but it appears we end up giving our moms something in return and that something can end up in her brain.

It’s called “reverse inheritance.” New research done by the Fred Hutchinson Cancer Research Center has proven how the process of pregnancy is even more complicated and bizarre than we were taught in health class.

Dr. Lee Nelson, with Fred Hutch, says for decades it was thought that the placenta was a kind of “biological firewall,” allowing the passage of some of the mother’s cell and nutrition while keeping the fetus’ cells from passing through to mom. Doctors believed that is what allowed the mother to grow a genetically foreign, and possibly hostile, organism inside her body.

Now, Nelson says the previous belief is false: Cells containing the fetus’ DNA do migrate into the mother. “There is control, there aren’t lots of cells moving from the fetus to the mother, but there are some.”

Nelson and Dr. William Chan found that some of those cells get as far as mom’s brain and remain there.

“The cells from the fetus can acquire a neuronal phenotype,” says Nelson. “Which means they aren’t just circulating blood cells, but they can differentiate and become a neuron within the brain.”

Researchers found that as a result, 63 percent of their female test subjects actually had cells with male DNA in their brain, most likely because they “reverse inherited” them from male children.

Presumably female fetuses do the same thing, but Nelson’s testing sought out the more easily distinguishable male DNA.

If that seems strange for the mother, think about the repercussions for the fetus. What your mother picks up from earlier children, then could be passed to you.

“You can get cells from an older sibling, you can even get cells from a twin that might have been lost in an earlier pregnancy. If your mother had an non-irradiated blood transfusion, she might have picked up DNA in cells from the donor,” Nelson says.

It generates a whole host of questions: Who is really doing your thinking? Who should you thank, or blame, for the size of your nose or the color of your eyes?

Follow up research will focus on the health effect of “reverse inheritance” on mothers.

Nelson says so far, it looks like the genetic two-way street is linked to auto-immune diseases and cancer – sometimes for better and sometimes for worse. In some cases such as breast cancer, fetal cells are thought to confer protection. When it comes to colon cancer, it appears to incur greater risk.

The next time your mother starts reminding you of all that she’s given you, you can tell her that you did give her something back – and it might be part of her brain.