Sporadic ALS

About 90% of cases of amyotrophic lateral sclerosis (ALS) — the progressive neurological disorder associated with the loss of motor neurons, the nerve cells that control movement — occur in patients with no family history of the disease.

These cases are known as sporadic ALS, and occur randomly. In the remaining 10% of patients, the disease affects multiple people in the same family, and is called familial ALS.

The causes of sporadic ALS are not well-understood. It is thought that a complex interaction between genetics and environmental factors leads to the development of the disease. Various genetic, biological, and environmental risk factors for sporadic ALS have been identified.

Genetics and sporadic ALS

While a person’s genes are thought to contribute to the development of sporadic ALS, the role of genetics in the disease remains poorly understood. It is likely, researchers say, that many small genetic variations all interact to affect a person’s risk of developing the disease.

It’s estimated that only about 10% of patients with sporadic disease carry a genetic mutation that is known to be associated with familial ALS.

Because of this, genetic testing generally is not routinely done in people with sporadic ALS, since the likelihood that such testing will yield useful information is quite low.

Risk factors

The most well-validated risk factor for developing sporadic ALS is age: the disease most commonly manifests — causes symptoms — between the ages of 40 and 70. Among younger patients, ALS is more common in males than females, though this sex-based difference disappears after about age 65.

Smoking cigarettes is another known risk factor for sporadic ALS. Exposure to other environmental toxins, as well as infections and injuries (especially head injuries), also may influence the disease’s development.

Certain professions, particularly the military and professional sports, are linked with a higher risk of ALS, though the reasons for these connections are not clear.


Last updated: Nov. 16, 2021


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