The disorder affects muscles used for movement.It causes muscle weakness that ranges from barely noticeable to very severe.

Some types of mitochondrial myopathy are inherited, while some are sporadic but both often occur before age 20.

ALS is often called Lou Gehrig's disease, after the baseball player who was diagnosed with it.

Worldwid 1 in 2,500 people are affected by these inherited neuromuscular diseases.

There are many scenarios in which stem cells have been used to delay rare diseases.

Dermatomyositis is most common in adults between ages 40 and 60, or in children between ages 5 and 15.