A quick test: Close your eyes for a second and try touching your nose.
Did you do it? Good. The reason you could — why you could find your target even without seeing it — is because of something called proprioception, the instinctual awareness of your body’s position in space. The world disappears when you close your eyes, but your sense of your own body doesn’t.
Except, in a very small number of people, it does. As Science reported today, scientists have identified two people, a 9-year-old girl and a 19-year-old woman, who seem to totally lack proprioception — the result of a genetic mutation that may shed some more light on how how and why we move the way we do.
The patients: The girl and the woman, both patients of neurologist Carsten Bönnemann at the National Institutes of Health, “shared a suite of physical symptoms, including hips, fingers, and feet that bent at unusual angles,” Science wrote. “They also had scoliosis, an unusual curvature of the spine. And, significantly, they had difficulty walking, showed an extreme lack of coordination, and couldn’t physically feel objects against their skin.”
The problem: The most intriguing symptom, though, made itself apparent when Bönnemann and his team blindfolded the patients. With their vision obstructed, they couldn’t walk in a straight line without tripping. They couldn’t move their finger from their nose to a point in front of their faces. When the researchers pulled their subjects’ arms up and down, the subjects couldn’t tell which direction the limbs were moving. In short, it was as if they relied entirely on sight to help them figure out how to move.
The diagnosis: When the researchers sequenced the patients’ genomes, they discovered that they shared the same mutation on a gene called PIEZO2, which controls touch and motion. Together, the woman and the girl are the first documented cases of this specific mutation in humans, though the researchers speculated that more may come out of the woodwork now that it’s been discovered.
And now that it has, they plan to investigate the role it plays in people with normal senses of proprioception, too. It may be possible that different mutations on this gene help to determine a person’s overall movement style — their grace and athleticism, or lack thereof. “Could a finely tuned PIEZO2 gene contribute to superior athletic performance, or a poorly tuned one to clumsiness?” Bönnemann said to Science. “I think it’s not impossible.”
Neither, as these two patients have proven, is getting through life without proprioception, a sense that was previously considered indispensable. They’ve learned to use their sight to compensate, allowing them to do the same physical tasks as anyone else — as long as they keep their eyes open.