Brain & Nervous System Health Center

Understanding ALS -- the Basics

What Is Amyotrophic Lateral Sclerosis?

In the U.S., amyotrophic lateral sclerosis, or ALS, is often called Lou Gehrig's disease after the famed baseball player whose struggle with this disease and death in 1941 brought it national attention.

ALS is an incurable, progressive degenerative neurological disorder. For reasons that are not understood, the nerve cells of the brain and spinal cord that control voluntary muscle movement gradually deteriorate. As a result, muscles waste away, leading to paralysis and death, usually in two to five years.

The only nerve cells affected are the lower motor neurons, which control a wide range of things like movement of your limbs, swallowing, and even some aspects of breathing. But the senses and thinking processes remain normal. Pain is rare in this disease at any stage.

The disease is relatively rare: About 5,000 new cases are diagnosed in the U.S. each year. It almost always strikes after the age of 40, and it affects more men than women.

What Causes ALS?

Although the cause of ALS is unknown, heredity plays a role in 5% to 10% of cases. A fraction of all cases of familial ALS (that is, inherited ALS) is believed to be caused by a defective gene that prevents the body from producing a normal amount of an enzyme called superoxide dismutase. This enzyme helps neutralize free radicals -- highly reactive oxygen molecules produced during metabolism and capable of damaging body tissues. Researchers speculate that defects in protective enzymes may also account for non-inherited ALS and that environmental toxins may be a factor.

Some evidence suggests that the disease may be triggered by exposure to heavy metals, animal hides, or fertilizers, although this is by no means proven. In addition, viral infection and severe physical trauma have been implicated as possible contributors. Other theories link ALS to a phenomenon called excitotoxicity, in which the nerve cells that control movement are overstimulated by a neurotransmitter called glutamate to the point where they eventually die.

WebMD Medical Reference Reviewed by Neil Lava, MD on March 19, 2015

Sources

SOURCES: 

Miller, R. Amyotrophic Lateral Sclerosis Edition 1, 2005. 

Cecil Textbook of Medicine (Single Volume) Edition 22, 2004.

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