Impotence is also known as erectile dysfunction. Most impotence is triggered not by genetic factors, but by obesity, diabetes, heart disease, smoking, drug and alcohol abuse, stress or anxiety. But in a paper published in the monthly journal Proceedings of the National Academy of Sciences, researchers say they found that a genetic variation at a locus in human DNA may increase a man’s risk of impotence by about 25 percent. They found statistical evidence after studying the genetic makeup of about 36,600 men, and confirmed it in a similar study of another 222,300 men. Subsequently, laboratory tests showed that the variation might affect the activity of a nearby gene that is linked to sexual function. Eric Jorgensen, a researcher at Kaiser Permanente, a major U.S. pharmaceutical company, and lead author of the paper, said scientists now want to explore how the variation could affect male impotence, and how it might interfere with the functioning of certain brain circuits. Finding a biological explanation may lead to clues for developing new impotence treatments.