Researchers at Johns Hopkins Medicine report that an experimental drug first developed to treat kidney disease prolongs survival and improves muscle function in mice genetically engineered to develop a severe form of Duchenne muscular dystrophy (DMD). According to the Muscular Dystrophy Association (MDA), DMD affects 1 in every 5,000 live male births and results in severe muscle wasting and weakness because of the lack of a protein called dystrophin, which is needed to strengthen muscle cells and protect them from mechanical injury. The dystrophin gene is in the X chromosome, so DMD mainly affects boys. Girls only get the disease if both X chromosomes are affected. Muscle symptoms begin between the ages of 2 and 4, and, by their early teens, most individuals with DMD are unable to walk. Dystrophin is also important to heart muscle, so heart failure often occurs in later teenage years into the early 20s. According to the MDA, people with DMD generally live until their late 20s or early 30s. There is no cure, but physical therapy and corticosteroids reduce inflammation and help delay muscle decline, helping symptoms, and improving quality of life. Newer gene-targeting treatments are being tested, but they remain limited to a small number of patients targeted.