The discovery shows nerves that detect pain and those that detect odors rely on the same protein to transmit information to the brain, ScienceNews.org reported Wednesday.

An international team of researchers examined three people who have mutations in the SCN9A gene and can't feel pain.

All of them had broken multiple bones without feeling any pain, and two had given birth painlessly, but none of the three was aware they also couldn't smell a thing, the researchers said in their study published in the journal Nature.

It's not unexpected that none of the people realized they lacked a sense of smell, experts said.

"If this was a genetic defect from birth they wouldn't even know what they were missing," Graeme Lowe, a neurophysiologist at the Monell Chemical Senses Center in Philadelphia who was not involved in the study, said.

Before this study scientists had been unaware smell and pain shared a common communication gateway.

The defect is in the SCN9A gene, which makes a protein involved in sending electrical signals to the brain, which interprets them as pain.

In the study, the team discovered odor-detecting nerve cells rely on the same protein.

Because of the missing protein, researchers say, messages sent by both pain- and odor-sensing nerves never actually make it to the brain.

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