Lou Gehrig's disease is a disorder that's also called amyotrophic lateral sclerosis (say: ah-my-uh-tro-fik lah-tuh-rul skluh-ro-sis), or ALS. The official name comes from these Greek words: 

•    "a" for without 
•    "myo" for muscle 
•    "trophic" for nourishment 
•    "lateral" for side (of the spinal cord) 
•    "sclerosis" for hardening or scarring 

So, amyotrophic means that the muscles have lost their nourishment. When this happens, they become smaller and weaker. Lateral means that the  disease affects the sides of the spinal cord, where the nerves  that nourish the muscles are located; and sclerosis means that the diseased part of the spinal cord develops hardened or scarred tissue in place of healthy nerves. 

ALS is often  called Lou Gehrig's disease after Lou Gehrig, a hall-of-fame baseball player for the New York Yankees who was diagnosed with ALS in the 1930s. People in England and Australia call ALS Motor Neurone Disease (MND). The French refer to it as Maladie de Charcot, after the French doctor Jean-Martin Charcot, who first wrote about ALS in 1869. 

What Is Lou Gehrig's Disease? 

Lou Gehrig's disease damages motor  neurons in the brain and spinal cord. Motor neurons are nerve cells that control muscle movement. Upper motor neurons send  messages from the brain to the spinal cord,  and lower motor neurons send messages from the  spinal cord to the muscles. Motor neurons are an important part of the body's neuromuscular system. The neuromuscular system enables our bodies to move and is made up of the brain, many nerves, and muscles. Things that we do every day —  like breathing, walking, running, lifting stuff,  and even reaching for a glass of water — are all controlled by the neuromuscular system. 

Here's how the neuromuscular system works: If  you want to make a fist,  your brain first sends signals through upper motor neurons to the area in your spinal cord that controls your hand muscles. Then lower motor neurons in your spinal cord signal the  muscles in your hand to move and make a fist. 

Over time, Lou Gehrig's disease causes these motor neurons in the brain and spinal cord to shrink and disappear, so that the muscles no longer receive signals to move. As a result, the muscles become smaller and weaker. Gradually the body becomes paralyzed (say: par-uh-lized), which means that the muscles no longer work. However, someone with ALS, even at an advanced stage, can still see, hear, smell, and feel touch.  The nerves that carry feelings of hot, cold, pain, pressure, or even being tickled, are not affected by Lou Gehrig's disease. The parts of the brain that allow us to think, remember, and learn are also not affected by the disease. 

Although this disease can strike anyone, it is extremely rare in kids. According to the ALS Association, most people who develop Lou Gehrig's  disease are adults between 40 and 70. Only 2 out of every 100,000 people will  get the disease each year. Because  it is not contagious, you can't catch ALS from someone who has the disease.
Among ALS cases in the United States, 5% to 10% are hereditary, which means the disease runs in certain families. This is called familial (say: fuh-mee-lee-ul) ALS. At least 90% of cases are not inherited; this is called sporadic (say: spuh-rah-dik) ALS.