How A Pregnant Woman's Choices Could Shape A Child's Health
Pregnant women hear a lot about things they should avoid: alcohol, tobacco, chemical exposures, stress. All of those have the potential to affect a developing fetus. And now scientists are beginning to understand why.
One important factor, they say, is something called epigenetics, which involves the mechanisms that turn individual genes on and off in a cell.
There's growing evidence that epigenetics is critical in determining a child's risk of developing problems ranging from autism to diabetes, says Dani Fallin, who studies the genetics of mental disorders at Johns Hopkins Bloomberg School of Public Health.
Epigenetic control of genes is part of what allows a tiny cluster of identical cells in the womb to grow into a fully formed baby. By switching certain genes on and off, some cells become heart cells while others become brain cells.
It's a delicate process that can be disrupted by exposure to certain chemicals or hormones, says Susan Kay Murphy, an associate professor of obstetrics and gynecology at Duke University School of Medicine. And the first week or so after conception appears to be "a particularly vulnerable time where environmental influences can directly affect an epigenetic outcome," she says.
Murphy's interest in epigenetics is personal as well as professional. She entered the field in the 1990s after her young son died from a rare form of liver cancer that has been linked to epigenetic changes. She also has a son with autism and a daughter with ADHD.
Much of what's known about the epigenetics of pregnancy comes from experiments with mice, specifically a group of genetically identical agouti mice. When these mice are exposed to certain chemicals or put on a special diet during pregnancy, it switches on the agouti gene in their offspring. That causes the pups to produce a lot of agouti protein, which turns their fur a striking yellow.
The agouti protein also prevents these mice from feeling full, no matter how much they eat, Murphy says. "So they become very obese and are predisposed to developing diabetes and cancer," she says
To learn whether something like that can happen in people, Murphy has been doing a study that looks at how a mother's environmental exposures and nutrition during pregnancy may be causing epigenetic changes in babies.
The study has already produced some interesting results involving folic acid, a vitamin many pregnant women take to reduce the risk of problems like spina bifida. "At the recommended levels, it's beneficial," Murphy says. "At very high levels you actually lose that benefit."
But the results of epigenetic changes don't necessarily appear at birth or even during childhood. That's because things that affect development very early in life can show up decades later, she says.
"If you think of development as a ball rolling down a creviced hill, there are many different paths that ball can take," Fallin says. "And epigenetic mechanisms may help shape that path."
So what happens in the womb may cause epigenetic changes that contribute to schizophrenia or diabetes decades later, she says.
Fallin is particularly interested in early developmental paths that can lead to autism. So she did a study looking at epigenetic information in the brain cells of children with autism and neurotypical kids.
"At specific places, we see differences in the brains from the autistic children," she says. "That's important because those particular genes may give us a clue about what's being turned on and off differently in autistic children."
A complete epigenetic explanation of autism or any other disease is a long way off, Fallin says. But in the meantime, epigenetic studies may help get the attention of pregnant women who would otherwise ignore recommendations about diet and behavior.
"If you see there is a detectable biological change because of exposure to drinking or because of exposure to smoking, that as a pregnant mom would convince me that, oh, it matters," she says.
Fallin has two children, and she hopes that epigenetic evidence will eventually make it clearer how much exposure is a problem during pregnancy. She says that might finally settle the question of whether it's OK for a pregnant woman to have a glass of wine with dinner.
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Transcript
STEVE INSKEEP, HOST:
It's MORNING EDITION from NPR News. I'm Steve Inskeep.
DAVID GREENE, HOST:
And I'm David Greene, good morning.
Today in Your Health, we're going to explore how genes and the environment shape intelligence of adolescents.
INSKEEP: And that's one of two stories we have on how nature and nurture interact. First, pregnant women hear a lot about how things like diet and smoking can affect a developing fetus. Now scientists are beginning to understand why.
NPR's Jon Hamilton reports on the emerging field of epigenetics.
JON HAMILTON, BYLINE: In the early 1990s, Susan Murphy was a mom and a graduate student studying microbiology. Then her older son who was still a toddler died from a rare form of liver cancer.
SUSAN MURPHY: And I made the decision then that following my graduate studies, I'd shift focus and work toward something that would contribute more to cancer research, to honor the memory of my son.
HAMILTON: That led Murphy to Duke University and to epigenetics. It's a field that studies how individual genes in a cell are switched on and off. This epigenetic switching is part of what allows a tiny cluster of identical cells in the womb to grow into a fully formed baby. During pregnancy, epigenetic instructions cause some cells to become heart cells and others to become brain cells.
It's a delicate process that can be disrupted if the cells are exposed to certain chemicals, including some found in cigarette smoke. And Murphy says there appears to be a critical period during the first week or so after conception.
MURPHY: That's usually before a woman even knows she's pregnant. And so, we think that that might be a particularly vulnerable time where environmental influences can directly affect an epigenetic outcome.
HAMILTON: And epigenetic changes have been linked to autism, diabetes, and even the cancer that killed Murphy's son.
Much of what is known about the epigenetics of pregnancy comes from experiments with mice, specifically a group of genetically identical animals known as Agouti mice. When these mice are exposed to certain chemicals or put on a special diet during pregnancy, it switches on the Agouti gene in their offspring. This causes the pups to produce a lot of Agouti protein, which turns their fur a striking yellow. And Murphy says that's just the beginning.
MURPHY: So not only are the mice yellow, but the Agouti protein also affects the satiety response of the mice, so that they never feel full. They continue eating and become very obese and are predisposed to developing diabetes and cancer.
HAMILTON: To learn whether something like that can happen in people, Murphy has been looking at how a mother's environmental exposures and nutrition during pregnancy can cause epigenetic changes in babies. Murphy says her work suggests there's something interesting going on with folic acid, a vitamin many pregnant women take to ward off problems like spina bifida.
MURPHY: At moderate levels, the recommended levels, it's beneficial. At very high levels you actually lose that benefit. So we aren't saying that it's harmful at high levels but the beneficial aspects of folic acid seem to be negated by having too much of it around.
HAMILTON: The results of epigenetic changes don't necessarily appear at birth. Dani Fallin of Johns Hopkins University says that's because things that affect development early in life can show up decades later.
DANI FALLIN: If you think of development as a ball rolling down a creviced hill, there are many different paths that ball can take by the time it gets to the end. It could end up very much to the left of where it started, very much to the right or in the center. And epigenetic mechanisms may help shape that path.
HAMILTON: So what happens in the womb may cause epigenetic changes that contribute to things like mental illness or heart disease in an adult. Fallin is particularly interested in early developmental paths that can lead to autism. So she did a study looking at the epigenetic information in the brain cells of both kids with autism and typical kids.
FALLIN: At specific places, we see differences in the brains from the autistic children than we do from the control children. That's important because those particular genes may give us a clue about what's being turned on and off differently in autistic children.
HAMILTON: Fallin says that's a long way off. In the meantime, she says, epigenetic studies may help get the attention of pregnant women who would otherwise ignore recommendations about diet and behavior.
FALLIN: If you see there is a detectable biological change because of exposure to drinking or because of exposure to smoking that, as a pregnant mom, would convince me that, oh, it matters.
HAMILTON: Fallin, who has two children, hopes epigenetic evidence will eventually make it clear how much exposure during pregnancy is safe. That might finally settle the question of whether it's OK for pregnant woman to have a glass of wine with dinner.
Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.
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