Treating Duchenne, the most common of the rare diseases

With an incidence of 1 out of 3,500 male births, Duchenne muscular dystrophy is one of the most common of the orphan or rare diseases. But, the effects of the disease, which causes death by the average age of 25, are some of the most destructive according to experts.

Orphan or rare diseases are defined in the United States as an illness that affects fewer than 200,000 people throughout the country. Duchenne is a subset of muscular dystrophy that occurs when a person has a genetic defect in which they cannot produce a protein that is present in muscle tissue, called dystrophin. It has the same worldwide incidence as it does in the United States, and may even have the same proportion of cases in the animal kingdom as well.

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Duchenne's patients are diagnosed around 3 or 4 years old, and normally don't show symptoms before they start exhibiting muscle weakness and are unable to keep up with their peers.

"It's pretty devastating," Eric Hoffman, the director of the Center for Genetic Medicine Research at Children's National Medical Center, said to CBSNews.com. "These boys are born normally, and don't show weakness until early school age. We just do a blood test and find astronomical levels of muscle leaking into the blood."

In addition to being one of the doctors who worked on the Genome Project and identified the gene that causes Duchenne, Hoffman is also a professor of pediatrics at George Washington University School of Medicine and Health Sciences in the District of Columbia.

Muscular dystrophy is the broad term for a group of inherited disorders that are caused by genetic defects. They range in severity and can affect some groups of muscles to all muscles and can progress at different rates.

For Duchenne's patients, they worsen pretty quickly, and their disease affects their whole body until they lose all muscular function, including that of the heart and lungs. By 8 to 12, boys stop walking on their own, and will need a ventilator by the time they reach 18 to 20.

"The disease has a pathway it follows that is a very predictable line," Michael Kelly, chief scientific officer of Cure Duchenne, told CBSNews.com.

However, with the help of steroid treatments, some Duchenne's patients are able to avoid wheelchairs until their 20s, and can live longer with the aid of a respirator, Hoffman said.

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Treating Duchenne, the most common of the rare diseases