Thankfully, smoking is a habit all pregnant women are advised to break. But, surprisingly, this wasn’t always the case, especially in the 1940s and 1950s when doctors endorsed smoking in tobacco advertisements. Tobacco companies even ran ads hinting that pregnant women could smoke as a way to calm their nerves. With the influx of research on the harms of cigarettes, it now seems absurd to think they were ever recommended. A recent study in American Journal of Human Genetics links maternal smoking to epigenetic changes that can negatively impact a mother’s child.
Epigenetics is a field of research that has recently gained significant momentum in the scientific community and popular culture alike. Various chemical modifications, such as DNA methylation or histone modification, occur to DNA as a result of environmental factors. These epigenetic modifications impact gene expression without altering the genetic sequence. Epigenetics is now contributing to the list of reasons why not to smoke, including dampening male fertility, which was described in our recent blog, Nicotine Could Cause Epigenetic Changes to Testes and Compromise Fertility.
In the very first paper from the international Pregnancy and Childhood Epigenetics (PACE) consortium, researchers investigated the epigenetic impact a pregnant mother’s smoking has on her child by conducting a genome-wide consortium meta-analysis. They studied 6,685 mothers and their newborns, comparing which genes were methylated. The fetus’ DNA largely mirrored patterns of methylated genes present in adults who smoke. In addition, the team identified new genes related to development that are impacted by maternal smoking.
“I find it kind of amazing when we see these epigenetic signals in newborns, from in utero exposure, lighting up the same genes as an adult’s own cigarette smoking. There’s a lot of overlap,” said Stephanie London, co-senior author of the study and a physician and epidemiologist at the National Institute of Environmental Health Sciences (NIEHS) of the National Institutes of Health (NIH). “This is a blood-borne exposure to smoking – the fetus isn’t breathing it, but many of the same things are going to be passing through the placenta.”
Mothers were grouped into sections depending on whether they smoked cigarettes occasionally while pregnant (25%), daily while they were pregnant (13%), or did not smoke at all (62%). The scientists used blood and umbilical cord samples from several different cohorts of newborns. The newborns with mothers who were sustained smokers, in other words, if their mothers smoked cigarettes daily during pregnancy, had their DNA differentially methylated in 6,073 locations compared to the newborns whose mothers did not smoke. Nearly half of these places could be pinpointed to a particular gene.
These genes were linked to nervous system and lung development, birth defects like cleft lip and palate, and smoking-related cancers. Many signals were linked to developmental pathways, according to the co-first author of the paper, Bonnie Joubert, an NIEHS epidemiologist. Using another analysis, these DNA modifications were still present in older children who were born to mothers who smoked.
Additional studies should build on the gene-expression analysis that these researchers conducted in order to better understand the underlying biological mechanisms that connect these epigenetic mechanisms to disease and child development.
“We already knew that smoking is related to cleft lip and palate, but we don’t know why. Methylation might be somehow involved in the process,” said London.
This initial study was conducted using PACE’s “consortium approach” — an approach that combines the efforts of several research teams to try to answer questions such as how a mother’s weight, her alcohol intake, and air pollution might affect the epigenetic marks of her child’s DNA, and how that, in turn, might impact his or her health. “It’s important to recognize the many people involved and the work that they did,” Joubert said.
Source: Joubert, B. et al. (2016). DNA Methylation in Newborns and Maternal Smoking in Pregnancy: Genome-wide Consortium Meta-analysis. American Journal of Human Genetics, 98(4): 680-696.
Reference: Cell Press. Mom’s smoking alters fetal DNA. EurekAlert. 31 Mar 2016. Web.