WASHINGTON, Sept. 24 (Xinhua) -- U.S. government researchers said they have found a gene that controls what could be our "sixth sense" beyond the basic five ones known as taste, smell, touch, sight and hearing.
It's called PIEZO2, which affects proprioception, or how our brain understands where our body is in space, according to researchers from the U.S. National Institutes of Health (NIH).
The discovery, published this week in the New England Journal of Medicine, was made with the help of two young patients with PIEZO2 mutations that caused them to have movement and balance problems and the loss of some forms of touch.
Actually, the gene involved was not a new discovery. Previously, scientists have found it generates electrical nerve signals in response to changes in cell shape, such as when skin cells and neurons of the hand are pressed against a table.
In this study, the two patients, one nine and the other 19 years old, are unrelated and have difficulties walking; hip, finger and foot deformities; and abnormally curved spines diagnosed as progressive scoliosis.
A series of examinations suggested the young patients lack body awareness. Blindfolding them made walking extremely difficult, causing them to stagger and stumble from side to side while assistants prevented them from falling.
When the researchers compared the two with unaffected volunteers, they found that blindfolding the young patients made it harder for them to reliably reach for an object in front of their faces than it was for the volunteers.
Without looking, the patients could not guess the direction their joints were being moved as well as the control subjects could.
The patients were also less sensitive to certain forms of touch. They could not feel vibrations from a buzzing tuning fork as well as the control subjects could. Nor could they tell the difference between one or two small ends of a caliper pressed firmly against their palms.
Brain scans of one patient showed no response when the palm of her hand was brushed.
Nevertheless, the patients could feel other forms of touch, such as the brushing of hairy skin. Stroking or brushing hairy skin is normally perceived as pleasant, but one of the patients claimed it felt prickly.
Despite these differences, the patients' nervous systems appeared to be developing normally. They were able to feel pain, itch, and temperature normally; the nerves in their limbs conducted electricity rapidly; and their brains and cognitive abilities were similar to the control subjects of their age.
These findings caused the researchers to believe that PIEZO2 is linked to proprioception and that when it is mutated people lose their "sixth sense".
They also concluded that the patients' scoliosis and joint problems suggest that the Piezo2 proteins are required for the normal growth and alignment of the skeletal system.
"Our study highlights the critical importance of PIEZO2 and the senses it controls in our daily lives," study leader Carsten Bonnemann, senior investigator at the NIH's National Institute of Neurological Disorders and Stroke, said in a statement.
"The results establish that PIEZO2 is a touch and proprioception gene in humans. Understanding its role in these senses may provide clues to a variety of neurological disorders."