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A pedestrian makes her way past downed trees as an ice storm ripped through Montreal on Jan. 6, 1998. The storm left over 600,000 people without electricity as ice-covered trees crashed down on power lines.Ryan Remiorz/The Canadian Press

The devastating ice storm of 1998 left a lasting impression, not just on the memories of those who lived through it, but on the DNA of children born in the aftermath.

Researchers at Douglas Mental Health University Institute and McGill University have followed more than 150 families after the storm, and found specific markers on the DNA of children whose mothers were pregnant with them or became pregnant soon after the disaster, providing rare evidence of how maternal hardships can have long-term genetic consequences.

The ice storm in January, 1998, is considered one of the country's worst natural disasters. It resulted in power outages across eastern Ontario and southern Quebec, forcing Quebec residents to brave the damage and severe cold without electricity and heat for up to six weeks. It also offered an unusual chance for scientists to examine the effects of maternal hardship on unborn children.

In a study, published online by the journal PLOS ONE, the researchers suggested that the level of objective hardships women experienced – such as the number of days they were without power and the damages to their homes – had a surprising impact on their children's genetic expression.

In June of 1998, the researchers recruited women who were pregnant during or became pregnant within three months of the storm, and asked them to complete two different questionnaires: one assessed the objective hardship they experienced, and the other measured their subjective distress related to the storm, assessing their post-traumatic stress-like symptoms, such as experiencing intrusive thoughts and images.

While the conventional thinking is that a mother's subjective distress, passed via elevated stress hormones through the placenta, would affect the fetus, researchers were stunned to find that the objective environmental factors also seemed to have a significant impact.

"Over the years, we found that that objective stress explained variance among kids – how kids varied one from another – in a whole host of things: IQ, language, BMI and obesity, insulin secretion, their immune system," says researcher Suzanne King, a professor of psychiatry at McGill University. (For the most part, these were negative, she says, although in the case of IQ and language, the relationship was found to be curvilinear.)

"So I wondered, like, how could this be?" she says. "How does a message get from the mother and her environment to the fetus if it's not going by the mom's distress and her stress hormones?"

The answer, the researchers found, can be explained by epigenetics. Here's how it works: An individual's genetics are like a musical score, and what's written comes from the mother and father, King explains. Although nothing can change what's written on the page, environmental factors act as an orchestral conductor might, amplifying some aspects and tempering others, leaving markings, or methylation of the DNA.

In 2011, when the children from the ice storm were aged 12 to 13, the researchers took blood samples from 36 of them, and examined the degree of methylation of their DNA. They found a correlation between the degree of DNA methylation and the degree of objective hardship the mothers experienced during the ice storm.

An important thing to consider is that the effects of these epigenetic changes aren't always necessarily negative, King says, explaining that the placenta can be thought of as a sensory organ, sending information from the mother to the fetus that will help preserve the fetus. For instance, she notes, during the Second World War, Dutch children whose mothers experienced famine during pregnancy were more likely to have diabetes, obesity and high blood-pressure as adults in peacetime.

"If they had been born into a famine, they would have been great," King says. "But it's because the postnatal environment was different than the prenatal environment, they were mismatched."

King and her fellow researchers are continuing to examine the effects of the ice storm on the group of children. Last year, they reassessed the children at age 15, and in a few months, they will be conducting brain imaging. These children could yet hold a wealth of untapped information.

"Nobody would've predicted that something like the ice storm would still be having these marks on the musical score 13 years later," King says. "So it's not only how large the effect is, but it's also the fact that it's lasted for 13 years."

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