A new study links neutral maternal behavior toward infants to stress-related epigenetic changes in children.
Epigenetics is a DNA-independent molecular process that affects gene behavior. In this study, researchers found that mothers’ neutral or hostile behavior with their children at 12 months was associated with epigenetic changes called methylation, or the addition of methane and carbon molecules, to a gene called NR3C1 when the children were 7 years old. This gene is involved in regulating the body’s response to stress.
“There is evidence of a relationship between the quality of the mother-infant interaction and the methylation of this gene, although the effects are small in response to relatively small differences in the interaction,” said Washington State University biological anthropologist and lead author Elizabeth Holdsworth. The study is published in the American Journal of Human Biology.
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Other studies have linked extreme stress in early life, such as neglect and abuse, to more dramatic methylation of this particular gene in adults. However, Holdsworth emphasized that the small differences indicated by this study may be indicative of normal human variation and that it is difficult to determine whether there are any long-term effects.
For this study, Holdsworth and her co-authors analyzed a subsample of 114 mother-infant pairs from the Avon Longitudinal Study of Parents and Children, a project that tracks a cohort of children born in 1991 and 1992 in Avon, UK.
The researchers first analyzed data from an observational study of mothers sharing picture books with their babies at 12 months, in which their interactions were coded as warmth. This study focused on mothers because they are often the primary caregivers of infants. The majority of women in this sample were white, college-educated, and from middle-income families. The range of warmth they showed differed only with the “coldest” behavior classified as awkward or neutral, but that’s exactly what the researchers hoped to test: that if even small differences in social interactions could be linked to epigenetic changes.
The observed behavior was then compared with data from epigenetic analysis of blood samples from children taken at age seven. The researchers found that mothers who showed hostile or neutral behavior toward their infants were associated with a small increase in methylation in the NR3C1 gene. This gene encodes a receptor involved in the regulation of the HPA axis – the interaction between the body’s hypothalamus, pituitary and adrenal glands. This axis plays a role in the stress response, including the production of the body’s primary “stress” hormone, cortisol.
The HPA axis can be activated by almost anything that requires a quick release of energy from reacting to real danger to simply exercising to watching a scary movie. The NR3C1 gene is known to be involved in activating this axis, but more research is needed to understand how methylation of that gene is related to the stress response, Holdsworth said, adding that some studies have shown increased methylation to be associated with hypo-reactivity, or a blunted response. while others have shown hyper-reactivity.
Researchers are working to figure out how these changes occur, especially during childhood when the body is developing rapidly — as well as what they might mean.
“Within developmental biology, we know that humans evolve to fit the environment they are in, which contributes to normal human biological variation. This is not necessarily good or bad,” she said. In addition to Holdsworth, the study includes co-authors. Lawrence Shell and Alison Appleton from the University at Albany, State University of New York. This research received support from the Biotechnology and Biological Sciences Research Council, the National Institutes of Health, the National Science Foundation and the Wellcome Trust.
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