Amyotrophic lateral sclerosis, also known as ALS and Lou Gehrig's disease, is a neurological illness characterized by progressive loss of voluntary muscle control. With ALS, the nerve cells that control the muscles die. Without these nerves, known as motor neurons, the brain can no longer control the muscles. ALS begins with muscle weakness and progresses to paralysis. Respiratory failure remains the leading cause of death among people with ALS, reports the National Institute of Neurological Disorders and Stroke. Three forms of ALS have been described.
Sporadic ALS
Of the approximately 20,000 people in the United States with ALS, approximately 90 to 95 percent have sporadic ALS, according to 2010 information from the National Institute of Neurological Disorders and Stroke. The term, sporadic indicates that the disease arises without an obvious cause. Family members of patients with sporadic ALS bear no increased risk for the disease. Sporadic ALS develops most frequently in adults between the ages of 40 and 60, with a slight preponderance of men. People of all races and ethnicities develop ALS. Although amyotrophic lateral sclerosis remains an area of active biomedical research, the disease is incurable. Many patients with ALS die within 3 to 5 years after symptoms of the disease begin, notes the National Institute of Neurological Disorders and Stroke.
Hereditary ALS
Approximately 1,000 to 2,000 people in the United States have the hereditary form of ALS, according to the National Institute of Neurological Disorders and Stroke. Many genetic mutations, or gene changes, can cause hereditary ALS. One form of hereditary ALS, also known as familial ALS, leads to an abnormality of the enzyme superoxide dismutase 1, or SOD1. This enzyme normally protects the body from damage caused by chemicals known as free radicals. Scientists are studying the relationship between poorly functioning SOD1 and the motor neuron loss that characterizes ALS.
The Washington University Neuromuscular Disease Center reports that patients with hereditary ALS often develop the disease earlier in adulthood compared to patients with sporadic ALS. Rarely, hereditary ALS may present during childhood or adolescence. The disease course and symptoms are otherwise similar with these two forms of ALS.
Guamanian ALS
An exceptional number of cases of ALS occurred in Guam and Papua New Guinea in the 1950s, notes the medical reference text "Harrison's Principles of Internal Medicine." The unexplained high incidence in a limited geographic region led investigators to speculate that an unidentified environmental factor may have contributed to the development of the disease, which scientists termed Guamanian ALS. Unlike patients with sporadic or hereditary ALS, people with Guamanian ALS usually develop mental deterioration, or dementia, and symptoms similar to Parkinson's disease. Although theories abound, the cause of Guamanian ALS remains unclear.
References
- National Institute of Neurological Disorders and Stroke: Amyotrophic Lateral Sclerosis
- Washington University Neuromuscular Disease Center: Hereditary ALS
- "Harrison's Principles of Internal Medicine, 16th Edition"; Dennis L. Kasper, M.D., et al., Editors; 2004
- The ALS Association: What is ALS?
- New York-Presbyterian Hospital: Amyotrophic Lateral Sclerosis (ALS)
