Canadian researchers have determined that prenatal maternal stress can permanently alter the DNA of children, Neomatica reports.

Studies carried out on animals have yielded similar results, but “human research is hampered by the lack of experimental methods that parallel controlled animal studies,” the researchers wrote, because subjecting pregnant women to stress levels capable of having an epigenetic effect on their children violates medical researchers ethical standards.

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“Disasters, however, provide natural experiments that can provide models of prenatal stress.”

So Lei Cao-Lei and Suzanne King, both of the Department of Psychiatry at McGill University, took advantage of one of the worst natural disasters in Canadian history — the Great Ice Storm of 1998 — to study the effect of severe hardship on pregnant women.

Shortly after the storm, the researchers recruited 176 pregnant women to participate in what they call now Project Ice Storm. They assessed their degree of objective hardship — how long they were without electricity — as well as their subjective distress.

Thirteen years later, they tested the genes of 36 of the children born of these women to see whether objective hardship or subjective distress had an effect on them.

How stressed the women felt during the 1998 ice storm turned out to have no effect on the DNA profiles of their children. However, objective hardship — the number of days a woman was deprived of electricity — had a strong correlation to changes in genes related to immune function.

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The researchers determined that the number of days an expectant mother was deprived of electricity created a change in their children’s immune systems that was “consistent with a change in gene programming of the immune system itself in response to stress.”

The children inherited an immune system that was, in essence, responding to the prenatal stress experienced by their mothers.