Researchers at Northwestern University say they’ve made a breakthrough discovery that could lead to a treatment for Lou Gehrig’s disease.

Amyotrophic lateral sclerosis, also called ALS, is a fatal neurodegenerative disease that slowly paralyzes its victims. Until now, scientists didn’t know exactly how it worked. But researchers at Northwestern’s Feinberg School of Medicine say they’ve found the culprit: the mutated version of a protein called ubiquilin2. Ubiquilin2 normally carries away other damaged or abnormal proteins.

But in someone with ALS, it doesn’t, and the bad proteins build up in the parts of the brain and spinal cord that control movement. Researchers say this is the first time scientists have identified a body process that’s involved in all types of ALS.

“This is very helpful and hopeful for the entire community,” said Teepu Siddique, the study’s lead author and a professor of neurology and clinical neurosciences. “And with the proper application of research, I think we can make rapid progress.”

Now that scientists have identified the mechanism that drives ALS, they can begin testing drugs to fight it, Siddique said. The study appears in the journal Nature.