Can a series of blows to the head lead to amyotrophic lateral sclerosis (ALS)? If so, how frequent and jarring must the injuries be to trigger the disease? Two studies at Cedars-Sinai have provided some early answers and guidance for future research.

“It has become increasingly clear in the past few years that brain injuries very likely play a role in the development of some cases of neurodegenerative disorders, such as Parkinson’s and Alzheimer’s diseases,” says Eric Ley, MD, a trauma surgeon in the Department of Surgery, director of the Surgical Intensive Care Unit, and one of the leaders of this research. “In these studies, we’re looking specifically at possible links between head trauma and ALS.”

Ley and co-investigator Gretchen Thomsen, PhD — who directs the Thomsen Laboratory in the Board of Governors Regenerative Medicine Institute — lead a team of researchers focused on examining such connections by using rats engineered with a genetic mutation that also is associated with ALS in humans.

One study found that a moderate-to-severe, single-episode brain injury did not hasten the onset of ALS. A second study, however, revealed that recurrent, mild injuries to both sides of the brain — like those seen in humans suffering repeated concussions — brought on earlier development of ALS in those with the predisposing mutation.

ALS damages motor neurons, leading to muscle atrophy and paralysis. Patients rarely live more than five years after onset. Although a small percentage of patients have a known genetic risk, the majority of cases are “sporadic” and of unknown origin. Members of the military, workers in certain industries, and participants in contact sports appear to be at higher risk for the condition.

“We do not understand all the factors that contribute to development of ALS, or why one person is susceptible and another is not,” Thomsen says. “We believe this research can provide an understanding of the effects of head injury on professional athletes, military personnel, and those who are predisposed to ALS and other neurodegenerative diseases.”