Stress have long-lasting effect on human body. Prenatal maternal stress is shown to have many negative effects in the offspring, some lasting in to adulthood. Stress can bring about epigenetic changes , like DNA methylation.It is unclear which aspect of stress is the active ingredient in these changes. Is it the objective severity of stress that matters? Or is it the cognitive appraisal of the stressor, or the subjective degree of distress?
How can you study this question? You need a major independent stressor affecting a large population to control for genetic bias and to differentiate the objective degree of exposure to an event from the cognitive appraisal and subjective degree of distress.
January 1998 ice storm in Quebec offered such an opportunity and was used to examine this issue. This project ( project Ice storm) have already shown that higher levels of maternal stress is associated with poorer physical, behavioral, motor and cognitive measures among the offspring from those pregnancies. DNA methylation levels among offsprings at age 13 higher and correlated with maternal objective stress.
The team now try to address whether cognitive appraisal ( as reported by participants in 1998: about the overall consequences of the ice storm on them and their families, and to provide a rating on a five-point scale from very negative to neutral to very positive) is correlated with DNA methylation at age 13.
Among 218 women who completed the assessments in 1998, nearly 35% rated the effect of storm as negative and 65% rated the effect as neutral or positive. The three aspects of the stress experience (the objective hardship, the cognitive appraisal of the storm’s consequences and the enduring subjective distress) were relatively independent of each other. At age, 13, offsprings blood study showed that 2872 candidate genes were significantly differentially methylated between these two appraisal groups. These are mostly those involved in immune function. Some changes were uniquely associated with maternal cognitive appraisal of the ice storm, and not with their objective exposure.
So, mothers cognitive appraisal of the situation is transmitted to the unborn child and this is perhaps NOT through the subjective stress and its physiological effects. Cognitive appraisal may have direct effect on stress hormone release.
Study has a small sample size.It is possible that the studied aspect of stress might have affected other areas of child development resulting in observed methylation changes.Peripheral DNA methylation is studied, this may not be truly reflective of brain levels.
This is the first human prenatal maternal stress study investigating the effect of maternal cognitive appraisal from an independent stressor that detects DNA methylation differences throughout the genome in the offspring during adolescence.
Summary of the article:
Pregnant women’s cognitive appraisal of a natural disaster affects DNA methylation in their children 13 years later: Project IceStorm. Cao-Lei L, Elgbeili G, Massart R, Laplante DP, Szyf M, King S. Transl Psychiatry. 2015 Feb 24;5:e515.