ALS: Amyotrophic lateral sclerosis. ALS has two meanings. One meaning of ALS refers to several adult diseases characterized by progressive degeneration of motor neurons. (In the UK, the term "motor neuron disease" is used for these disorders.) The second meaning of ALS refers to a specific form of motor neuron disease in which there are both upper and lower motor neuron signs.

Motor neuron diseases such as ALS are progressive chronic diseases of the nerves that come from the spinal cord and supply electrical stimulation to the muscles. This stimulation is necessary for the movement of body parts.

Amyotrophic lateral sclerosis is quite a mouthful. The disease is therefore usually referred to simply as ALS or in North America as Lou Gehrig's disease after the great baseball player who died of it.

ALS strikes in mid-life, most often in the fifth through seventh decades of life. Men are about one-and-a-half times more likely to have the disease as women.

ALS occurs when specific nerve cells in the brain and spinal cord that control voluntary movement gradually degenerate. The loss of these motor neurons causes the muscles under their control to weaken and waste away, leading to paralysis.

ALS manifests itself in different ways, depending on which muscles weaken first. Symptoms may include tripping and falling, loss of motor control in hands and arms, difficulty speaking, swallowing and/or breathing, persistent fatigue, and twitching and cramping, sometimes quite severely.

There is no cure for ALS; nor is there a proven therapy that will prevent or reverse the course of the disorder. The Food and Drug Administration (FDA) approved riluzole, the first drug that has been shown to prolong the survival of ALS patients. Patients may also receive supportive treatments that address some symptoms.

ALS is progressive and fatal. The usual causes of death of patients with motor neuron diseases are not directly related to the disease, but result from simultaneous additional illnesses which ultimately occur because of weakness of the body. These illnesses are often infections. ALS usually leads to death within 5 years of the time the diagnosis of ALS is made; the range is from 2 to 7 years.