Imagine a mouse with bulky muscles and a bulging physique able to leap a single bound over a labyrinth’s maze. Welcome the new breed of Mighty Mouse with more than twice the normal amount of muscle mass. Thanks to Dr. Se-Jin Lee of John Hopkins University, it’s considered one of the most important discoveries in modern medicine. The mice, described today in the journal Nature, owe their bulging physiques to the lack of a gene that would normally limit muscle growth. The function of the gene was previously unknown, and its discovery, by a team led by Dr. Se-Jin Lee of Johns Hopkins University, is considered an important advance. A new breed of mice with more than double the normal amount of muscle may lead to meatier chickens and cows and, eventually, new treatments for people with muscle diseases, researchers are reporting.