People with Lou Gehrig’s disease, or ALS, are more likely to have been exposed to toxic pesticides or to have served in the military than similar people without the condition, according to a new study.

ALS, or amyotrophic lateral sclerosis, is a degenerative disease in which nerve cells break down over time. ALS affects fewer than 20,000 people in the U.S. each year, according to the Mayo Clinic.

The disease is progressive, eventually affecting the ability to chew, swallow, speak and breathe. In 2014, the ALS “Ice Bucket Challenge” went viral on the internet and helped raise $115 million for research toward a cure.

“The environmental risk of ALS has been a concern for many years,” said senior author Dr. Eva L. Feldman of the Alfred Taubman Medical Research Institute at the University of Michigan in Ann Arbor.