Photo: Robert Waterland and technician Eleonora Laritsky measuring DNA methylation. Link to photo informationIt’s undeniable that mothers have a tremendous impact on their children’s lives, but now research suggests that the impact can even extend to how certain genes function in those children as a result of the mother’s nutritional status at the time she becomes pregnant.
This story starts in three rural villages in the West African nation of The Gambia, where food is generally less available during the peak rainy season of August and September than during the drier months of March through May. The research was conducted by scientists with the Agricultural Research Service (ARS), and it indicates that the functioning of certain genes in children who were conceived during the rainy season is different from that in children conceived during the dry season.
The key component is a relatively new science called epigenetics. Epigenetic mechanisms don’t change the DNA sequence of our genes, but they do cause changes in the way those genes function, and that variation appears to be permanent.
Although epigenetics was at one time highly controversial, these days it’s accepted as likely having a role in human disease, including cardiovascular disorders, type 2 diabetes, obesity and even certain types of cancer.
The ARS scientists’ work focused on one particular epigenetic mechanism called “DNA methylation,” which plays a key role in the development of different cell types in the body.
Results of earlier ARS studies with laboratory animals strongly suggested that due to epigenetics, if an expectant mom is overweight when she conceives, or even if she’s overweight before she becomes pregnant, that could affect the baby’s ability to regulate his or her weight. This “maternal programming” of the unborn child and the developing newborn could increase the risk that the child will grow up to be an overweight or obese adult.
In that lab animal study, mice born to mothers that had been fed a diet designed to increase DNA methylation did in fact have higher DNA methylation levels at certain genes. The Gambian study is the first to show this influence can occur in humans, too.
In the Gambian study, blood samples from 50 healthy Gambian kids were analyzed to detect differences in the level of DNA methylation at specific regions of certain genes.
The ARS scientists were able to show that levels of DNA methylation of five specific genes were higher in children who were conceived during the peak rainy season than the levels in the other children. At least two of those five genes are associated with risk of disease. One of the genes, SLITRK1, is associated with Tourette’s syndrome, and the PAX8 gene is associated with hypothyroidism.
In the study with mice, the effects of the mother’s nutrition on DNA methylation levels were permanent. In the Gambian study, because the youngsters were tested when they were about 9 years old, the scientists think the epigenetic effect will also be permanent.
So where does the rainy season come into play? The three Gambian villages where the ARS scientists focused on the nutritional status of the women during the “periconceptional period”—from before the women conceived until early in their pregnancy—are in an area where there’s no irrigation, so farmers must rely on rainfall to water their crops.
They plant their staple crops like corn, rice and millet only at the beginning of the rainy season, and harvest at the end—and those foods could be in very short supply, if not altogether gone, before the next harvest rolls around. Also, it’s hard work to plant, tend and harvest those crops, so the people of the village are burning more calories than they’re taking in.
But there are unresolved mysteries in the study results. For example, the scientists thought that peak rainy season hunger would lower the levels of DNA methylation in children conceived at that time, but they found exactly the opposite. They don’t know why that happens, but they’re hoping additional studies will provide some answers.
It’s frightening—and amazing—to think that something as simple as the weather at the time of conception could have a lifelong impact on a child. But looking behind that door, exploring the potential of epigenetics, could give us a much better chance of ensuring a healthy life for that child and many more.
The Agricultural Research Service is the chief in-house scientific research agency of the U.S. Department of Agriculture. You can read more about ARS discoveries at http://www.ars.usda.gov/news/.