Only one in 100 women has the variant, which reduces the ability of nerve cells to send pain signals to the brain, researchers at the University of Cambridge found.
The gene then acts as a natural epidural and may explain why childbirth is a less painful experience for a small number of women.
The scientists put a group of women, all of whom gave birth without asking for pain relief, through a series of exercises to assess their resistance to discomfort, including applying heat and pressure to the arms and asking them to dip your hands in ice cold water.
Compared to another group of mothers who did require pain relief, they were shown to have a much higher threshold before experiencing pain.
“It is unusual for women to not request gas and air, or an epidural to relieve pain during labor, particularly when they give birth for the first time,” said Dr. Michael Lee, joint lead author, in a press release.
“When we tested these women, it was clear that their pain threshold was generally much higher than for other women,” said Lee, a professor in the division of anesthesia at the University of Cambridge.
Then her genetic code was explored, and scientists found a unique variant for a cell that was present in many of the women who didn’t need help during labor.
It involved the KCNG4 gene, which helps make proteins that created a “gate,” controlling the electrical signal that flows through our nerve cells and into our brains.
“The sensitivity of this gatekeeper to electrical signals that had the ability to open the door and activate nerves was reduced by the rare variant,” the researchers found.
“The genetic variant we find in women who feel less pain during labor leads to a ‘defect’ in the switch formation of nerve cells,” explained co-author Ewan St. John Smith. “In fact, this defect acts as a natural epidural.”
“It means it takes a much larger signal, in other words, stronger contractions during labor, to turn it on,” said Smith, a PhD in the Cambridge department of pharmacology. “This makes it less likely that pain signals can reach the brain.”
“We have not only identified a genetic variant in a new player that underlies different pain sensitivities,” added co-author Frank Reimann, professor of endocrine signaling in the Cambridge department of clinical biochemistry. “But we hope this can open the way for the development of new drugs to control pain.”
Their study was published in the journal Cell Reports on Tuesday.
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