Chronic pain is an unknown issue with unknown causes and a subjective definition but some people clearly have it. Researchers recently analyzed 2,721 people, all taking prescription opioid pain medications, for genes COMT, DRD2, DRD1 and OPRK1. The participants also rated their perception of pain on a scale from zero to 10. People who rated their pain as zero were not included in the study.

Low pain perception was defined as a score of one, two or three; moderate pain perception was a score of four, five or six; and high pain perception was a score of seven, eight, nine or 10. 

9 percent of the participants had low pain perception, 46 percent had moderate pain perception and 45 percent had high pain perception.

Based on the results, the researchers believe they have identified key genes linked to why some people have a higher tolerance for pain than others. They found that the DRD1 gene variant was 33 percent more prevalent in the low pain group than in the high pain group. Among people with a moderate pain perception, the COMT and OPRK variants were 25 percent and 19 percent more often found than in those with a high pain perception. The DRD2 variant was 25 percent more common among those with a high pain perception compared to people with moderate pain.  "Our study is quite significant because it provides an objective way to understand pain and why different individuals have different pain tolerance levels," said study author Tobore Onojjighofia, MD, MPH, with Proove Biosciences and a member of the American Academy of Neurology. "Identifying whether a person has these four genes could help doctors better understand a patient's perception of pain. 

"Chronic pain can affect every other part of life. Finding genes that may be play a role in pain perception could provide a target for developing new therapies and help physicians better understand their patients' perceptions of pain."