Why some people react with a mild "Ouch" to injuries that can cause screams from others is linked by researchers to a single gene that controls pain sensitivity. The discovery may allow doctors to prescribe drug medication to precisely match the pain thresholds of patients suffering from injuries, cancer or such chronic conditions as arthritis, said Dr George Uhl, lead researcher of a study in the Proceedings of the National Academy of Sciences. "Now people can think of pain as a genetically regulated problem," Dr Uhl said. "This will help us learn how to treat long-term pain."