Researchers Tackle Complexity of Intergenerational Stress Transmission
The timing and mechanisms that account for the transmission of stress from parent to child remain challenging even as progress is being made.
Before, during, or after? Those are the questions facing researchers studying the transmission of stress from one generation to another.
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“Altogether, far less controversy regarding intergenerational transmission of stress exists today, as transmission has been documented across species, cultures, and trauma types and for a variety of psychiatric disorders,” wrote Mallory Bowers, Ph.D., and Rachel Yehuda, Ph.D., of the Icahn School of Medicine at Mount Sinai in New York. Yehuda is a professor of psychiatry and neuroscience, and Bowers is a postdoctoral fellow in psychiatry.
The big question, they said, is how that process takes place. Several hypotheses have been suggested, but they are not mutually exclusive, and more than one mechanism may be at work. In addition, the roots of transmission may lie before conception, during gestation, or following birth, they said.
“Across species, studies suggest that the effects of parental stress can be directly transmitted to offspring via gametes, uterine environment during pregnancy, or during early postnatal care of newborns,” they wrote in the January issue of Neuropsychopharmacology.
Such transmission goes beyond mere genetic inheritance or the more conventionally observable influence on the child of a parent’s behavior or actions.
The first question they addressed was whether the effects of a stressful event that the parent experiences before the child is conceived can be transmitted biologically.
Prenatal cortisol levels have been associated with offspring cortisol levels, but whether that correlates with parental stress is still unclear, they said. Alternatively, circulating cortisol during pregnancy might directly or indirectly affect the fetus.
Epigenetic processes, such as methylation of NR3C1, which encodes the glucocorticoid receptor, have shown cross-generational associations. The serotonin transporter gene SLC6A4 is under investigation as a possible moderator of risk for offspring psychopathology.
Neuroanatomical effects have been noted as well. Researchers report that prenatal maternal anxiety has been tied to a reduction in gray matter volume in the prefrontal cortex and in the frontal cortical thickness of offspring. Postnatal maternal anxiety may also influence hippocampal growth, they said.
“These studies suggest that maternal prenatal stress could establish early structural changes in these regions that precede later clinical problems in offspring.”
Several methodological problems need to be addressed if the field is to make progress, said Bowers and Yehuda. Terminology must be clarified “to distinguish between parental biology and parental behavior as mediators of offspring effect.” Also, objective and subjective evaluation of stress must be differentiated, as well as the difference between stress and psychopathology.
The fact the parents and children usually share a common environment is another potential confounder, they said. “Disentangling parent/offspring shared environmental stressors from transmitted stress is likely to be complex.”
Most of the research has examined the maternal side of ancestry, but fathers may be due for a closer look, too.
Some factors like supportive relationships and maternal warmth seem to mitigate some of the possible intergenerational results of stress, they said. “However, it is not clear whether these mitigating factors ‘erase’ or otherwise prevent the biological signatures in offspring of parent stress.”
In conclusion, said Bowers and Yehuda, “the field is ripe for addressing a multitude of hypotheses.”
Those hypotheses can be tested by further recourse to animal studies on the one hand and large human cohorts on the other, along with the use of rigorous statistical methods and “identified gold standard techniques,” they said. ■
An abstract of “Intergenerational Transmission of Stress in Humans” can be accessed here.
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Published online: 14 January 2016
Published in print: January 2, 2016 – January 15, 2016
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