During its brief existence, the placenta is a workhorse of an organ.
That’s because the fetus growing inside is entirely reliant on the placenta, which performs a dizzying array of functions (supplying oxygen, food and more) that will later be divvied up among the liver, kidneys, gut and lungs.
Given how central the placenta is to human development, though, it’s relatively poorly understood, scientists say — and a new study published Monday in Nature Medicine has revealed that the placenta has another, more surprising role: Its health is linked to the risk of developing schizophrenia, particularly in those who already have a higher genetic risk for the disorder, according to Johns Hopkins University researchers.
Up to 70 percent of a person’s risk for schizophrenia is based on genes, according to the National Institutes of Health. But whether or not those genes are “turned on” or left unexpressed is in part related to complications during pregnancy, the new study says.
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The team of researchers collected genetic tests from more than 2,800 adults around the world, including in the U.S., Europe and Asia. Of those participants, 2,038 had been diagnosed with schizophrenia. And for all of the participants involved, investigators looked into how their mothers’ pregnancies went, researchers said.
That led to the key finding: For people whose genes put them at risk for schizophrenia, being the product of a difficult or complicated pregnancy made the child at least five times more likely to develop the disorder, researchers found.
As many as 20 percent of all pregnancies include complications, Scientific American reports — ranging from restricted fetus growth or emergency Caesarean sections to issues with high blood pressure such as preeclampsia.
Once scientists connected pregnancy complications and placental stress with schizophrenia, they analyzed gene expression in placental tissue, including those that had complications like preeclampsia or intrauterine growth restriction. What they found was “a striking and consistent turning on of the schizophrenia genes” in those placentas. As more of those schizophrenia risk genes were “turned on,” raising the risk of developing the disorder, researchers found more inflammation and other hallmarks of distress, too.
“For the first time, we have found an explanation for the connection between early life complications, genetic risk, and their impact on mental illness and it all converges on the placenta,” Daniel R. Weinberger, the lead investigator on the study from the university’s Lieber Institute for Brain Development, said in a statement.
Other scientists agreed that the study is an important step in understanding how much of the disease is genetic, and how much is environmental.
“This should be an eye-opening study, especially for anyone who thinks disease risk is all genetic,” Janine LaSalle, a genetics researcher at the the University of California in Davis, told Stat. “Genes don’t exist in a lock-box away from everything else that happens to you.”
Researchers also said the study could provide clues about why men are as much as four times more likely to develop not just schizophrenia, but other disorders like dyslexia, autism and Tourette's Syndrome. Researchers discovered that the schizophrenia-linked genes activated during tough pregnancies were much, much more prevalent in male placentas than female placentas.
Researchers said the results are important because they could help doctors come up with new treatments and therapies, and “ultimately reduce the incidence of neurodevelopmental behavior disorders.”