Nausea and vomiting that often characterize the first trimester of pregnancy are mainly caused by a single hormone, study finds published Wednesday in the journal Nature. Researchers said the discovery could lead to better treatments for morning sickness, including in rare and life-threatening cases.

The study confirms previous research that pointed to the hormone GDF15. Researchers have found that the amount of hormones circulating in a woman’s blood during pregnancy, as well as her exposure before pregnancy, determines the severity of her symptoms.

More than two-thirds of pregnant women experience nausea and vomiting during the first trimester. And about 2% of women are hospitalized for a condition called hyperemesis gravidarum, which causes incessant vomiting and nausea throughout pregnancy. This disease can lead to malnutrition, weight loss and dehydration. It also increases the risk of premature birth, pre-eclampsia and blood clots, threatening the lives of the mother and fetus.

Perhaps because nausea and vomiting are so common during pregnancy, doctors often overlook hyperemesis, considering its serious symptoms psychological, even though it is the leading cause of hospitalization in early pregnancy. , according to experts. Although celebrities like Kate Middleton and Amy Schumer have raised awareness of the condition in recent years by sharing their experiences, the condition remains understudied.

“I’ve been working on this for 20 years and yet there are still reports of women dying from it and women being abused,” said Dr. Marlena Fejzo, a geneticist at the Keck School of Medicine at the University of Southern California. and co-researcher. author of the new study.

She personally knows the pain of this disease. During her second pregnancy, in 1999, Dr. Fejzo was unable to eat or drink without vomiting. She quickly lost weight, becoming too weak to stand or walk. Her doctor was dismissive, suggesting she was exaggerating her symptoms to get attention. She was eventually hospitalized and miscarried at 15 weeks.

Dr. Fejzo said she asked the National Institutes of Health to fund a genetic study of hyperemesis, but it was rejected. Undeterred, she convinced 23andMe, a popular genetic testing company, to include questions about hyperemesis in its surveys of tens of thousands of customers. In 2018, she published a paper showing that clients with hyperemesis tended to carry a variant of a gene for GDF15.

Hormones are chemicals that send messages throughout the body. GDF15 is released by many tissues in response to stress, like an infection. And its signal is very specific: the hormone receptors are grouped in a part of the brain responsible for nausea and vomiting.

In the new study, Dr. Fejzo and colleagues at the University of Cambridge in England measured the hormone in the blood of pregnant women and analyzed genetic risk factors for hyperemesis.

Researchers found that women with hyperemesis had significantly higher levels of GDF15 during pregnancy than those who had no symptoms.

But the effect of the hormone appears to depend on a woman’s sensitivity and her exposure to the hormone before pregnancy. Researchers found, for example, that women in Sri Lanka with a rare blood disorder causing chronically high levels of GDF15 rarely experienced nausea or vomiting during pregnancy.

“It completely erased all the nausea. They have virtually no symptoms during pregnancy,” said Dr Stephen O’Rahilly, an endocrinologist at Cambridge who led the research.

Dr. O’Rahilly hypothesized that prolonged exposure to GDF15 before pregnancy might have a protective effect, making women less sensitive to the surge in the hormone caused by a developing fetus.

In laboratory experiments, scientists exposed some mice to a small amount of the hormone. When given a much higher dose three days later, the mice did not lose their appetite as much as animals that had not received the previous dose, showing a robust desensitization effect.

The results offer hope for better treatments for hyperemesis, experts say. Patients with hyperemesis could one day take drugs to block the hormone’s effects in the brain, if clinical trials prove the drugs are safe during pregnancy. These drugs are tested in tests cancer patients with loss of appetite and vomiting also caused by GDF15.

It may even be possible to prevent this disease. Women at risk, such as those who experienced severe nausea and vomiting during a previous pregnancy, might be exposed to low doses of the hormone before becoming pregnant. (A diabetes drug, metformin, increases GDF15 levels and is already prescribed to promote fertility in some patients.)

The new study is powerful because it offers genetic evidence of a causal relationship between GDF15 and the disease, said Dr. Rachel Freathy, a geneticist at the University of Exeter who was not involved in the study. This will help this disease be better recognized, she said.

“A lot of people think women should just be able to cope with this,” Dr. Freathy said. With this biological explanation, she says, “you’ll be more likely to believe it’s a real thing rather than something in someone’s head.”

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