Risk factors

Established risk factors for ALS include:

• Heredity. Five to 10 percent of the people with ALS inherited it (familial ALS). In most people with familial ALS, their children have a 50-50 chance of developing the disease.
• Age. ALS risk increases with age, and is most common between the ages of 40 and the mid-60s.
• Sex. Before the age of 65, slightly more men than women develop ALS. This sex difference disappears after age 70.
• Genetics. Some studies examining the entire human genome found many similarities in the genetic variations of people with familial ALS and some people with noninherited ALS. These genetic variations might make people more susceptible to ALS.

Environmental factors, such as the following, might trigger ALS.

• Smoking. Smoking is the only likely environmental risk factor for ALS. The risk seems to be greatest for women, particularly after menopause.
• Environmental toxin exposure. Some evidence suggests that exposure to lead or other substances in the workplace or at home might be linked to ALS. Much study has been done, but no single agent or chemical has been consistently associated with ALS.
• Military service. Studies indicate that people who have served in the military are at higher risk of ALS. It's unclear what about military service might trigger the development of ALS. It might include exposure to certain metals or chemicals, traumatic injuries, viral infections, and intense exertion.