Don’t look down? Ah, forget that. By all means, look down. Gabriel Amador lives for the thrill, the adrenal rush, of scaling great heights at great personal danger and savoring the quest by peering into the abyss.

So there Amador stood last month, at the midpoint of a narrow bridge near the Mount Everest base camp during a 22-day trek through harsh Nepalese terrain. His guide and a Sherpa had already briskly reached the relative safety of the other side; Amador leaned over the railing for a peek.

“It was so cool to look down and see nothing below you,” says Amador in a matter-of-fact tone. “That’s when you feel the most alive.”

This 48-year-old pension administrator lives for such pulse-pounding experiences. And if you wonder about his motivation, you wouldn’t be the first. Last year, before he left on a trip to climb Mount Kilimanjaro, an astonished co-worker stopped by Amador’s desk to ask why he did it.

“There must be some type of gene I have,” he replied, “because I still love doing it.”

They laughed it off, but Amador may actually be on to something.

Genetic researchers are using DNA data and functional MRIs of the brain to try to pinpoint whether there really is a chemical basis to risk-taking, or its close cousin sensation-seeking, in extreme athletes.

No definitive study has been published, but most researchers are focusing on the dopamine DRD4 receptor, a genetic marker that controls the flow of chemicals to the brain’s reward center. Others have posited that risk-takers show a lower stimulus response in the brain’s amygdala region, which triggers fear response, than the average person.

Psychologists have long studied people’s personality traits and have determined that 10 percent to 15 percent of the population can be classified as Type T (for thrill), based on the Zuckerman-Kuhlman Personality Test. These people tend to seek out novel experiences, the theory being that they need to stimulate low dopamine levels.

Many of the studies have focused on sensation-seekers with drug and alcohol addictions or personality disorders. But a body of literature looking at sensation-seeking athletes is being developed.

As Terri Schneider, a sports psychologist and endurance athlete wrote in the 2007 Journal of Sport Behavior, “Choosing risk for the sake of risk is not the goal. Rather, while being attracted to activities that offer novel or intense experiences, sensation seekers are willing to accept the potential risks involved.”

Schneider is quick to add, though, her survey of adventure racers regarding sensation-seeking shows they “scored higher than mountaineers and rock climbers — and that’s pretty darn high.”

Cynthia Thomson, a former downhill skier and a risk-genetics researcher at the University of British Columbia in Vancouver, has had mixed results in looking at the DNA of 200 skiers and snowboarders who identify themselves as sensation seekers.

Thomson had participants fill out the Zuckerman personality questionnaire, then submit to a DNA test. She was looking for a genetic variant in the dopamine DRD4 receptor. She found a link — but only in female skiers.

Her theory: “There’s a lot of social influences for men. Sensation seeking is higher in men compared to women, but they also feel the (peer) pressure to exhibit that type of behavior, whereas there seems no such pressure on the females, so it may be more genetic in them.”

Thomson is testing other genes that may be involved in risk-taking, but her experience and lab results make her sure of one thing: “It’s always a combination of genetics and environment.”