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NIH Findings, March 2005

March 3, 2005 By —A.D.

Seeing Red

Hair color, like many other aspects of our appearance, is inherited. But genetic factors also influence less visible characteristics, such as how we respond to medicines.

Anesthesiologists have long observed that people with naturally red hair may need more anesthesia and have wondered if heredity plays a role. NIGMS grantee Daniel Sessler of the University of Louisville School of Medicine in Kentucky decided it was time to put the issue to the test.

Sessler, an anesthesiologist, recruited 10 women with naturally bright red hair and an equal number with black or dark brown hair. He gave the women a commonly used inhaled anesthetic, then applied a small electric shock to each woman’s thigh and watched for a reflex movement, an indication that the anesthetic dose was too low. The women did not feel or remember the shock.

Sessler adjusted each woman’s dose until she had a reflex movement only half the time, a standard method for determining the appropriate individual dose of an anesthetic medicine. He found that nearly all of the red-haired women needed 20 percent more anesthetic than did those with dark hair.

Just about all people with red hair share a common genetic variation that affects hair and skin color. After analyzing DNA from the women in the study, Sessler identified this genetic variation in 90 percent ofthe red-haired women who needed more anesthesia. In a separate study, he discovered that redheads also get less pain relief from local anesthesia, the kind you often get at the dentist.

While the study findings do not directly link hair color genes to anesthesia response, they do suggest that health care providers should monitor anesthesia doses carefully in redheads. More broadly, the research opens the door for further study ofthe role of heredity in anesthesia response.