Group Creates Engineered "Marathon Mice"

Researchers on Monday unveiled genetically engineered mice that can run farther and longer than their naturally bred brethren, bringing the "genetic doping" of elite athletes a small step closer to reality. The creation of the so-called marathon mice, announced Monday, follows earlier genetic engineering work that created "Schwarzenegger mice," rodents that bulked up after getting injected with muscle-building genes. The engineered mice racing away on their treadmills are bound to add to the furor over performance-enhancing substances, just as the world's best marathoners prepare for the Olympic event Sunday. The gene engineered in these mice essentially mimics exercise: Researchers say it conferred endurance and prevented the modified mice from becoming obese — even when they were kept inactive and fed a high-fat diet.

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