By Maggie Fox

WASHINGTON (Reuters) – Scientists reported on Tuesday they have some of the best evidence yet to support long-held theories that repeated blows to the head may cause nerve-degenerative diseases like Lou Gehrig's disease and Alzheimer's.

Autopsies of 12 athletes who died with brain or neurological disease showed a distinctive pattern of nerve damage – and fingered some potential culprits.

All had repeated concussions during their careers. Three of the men had been diagnosed with amyotrophic lateral sclerosis, also known as ALS or Lou Gehrig's disease, the star baseball player who died of it.

Experts in brain injury said the study, published in the Journal of Neuropathology & Experimental Neurology, pointed to new areas of research and possible ways to prevent long-term damage from concussions.

"if you could somehow give a person a drug, you could potentially prevent an illness like amyotrophic lateral sclerosis," Dr. Jeffrey Bazarian of the University of Rochester Medical Center in new York said in a telephone interview.

The findings also point to an urgent need to watch veterans of the wars in Iraq and Afghanistan, many of whom suffer brain injuries from explosions, accidents and blows to the head from other causes, the experts said.

"this is the first pathological evidence that repetitive head trauma experienced in collision sports might be associated with the development of a motor neuron disease," Dr. Ann McKee of Boston University School of Medicine and colleagues wrote in the report, available at link.reuters.com/fab65n.

McKee's team studied the donated brain and spinal cords of 11 professional football players or boxers and one hockey player. all had a newly characterized disease called chronic traumatic encephalopathy, or CTE, in which dementia set in years after repeated concussions.

PROTEIN CULPRIT

Three of the men also were diagnosed with ALS, a member of a family of diseases called motor neuron disease, which cause progressively worse paralysis.

The researchers looked specifically for a protein called TDP-43. they found it in the brain and in the spinal cords of the men – which could explain the ALS-like symptoms.

Scientists know that damaging one nerve can sometimes set off a cascade of other nerves dying, for reasons that remain poorly understood. TDP-43 could be involved.

Bazarian, who was on an Institute of Medicine Committee that released a report in 2008 linking concussions to later-life neurologic diseases, said the finding could help explain studies that show Iraq war veterans have a higher-than-normal rate of ALS, for example.

Drugs including the hormone progesterone, monoclonal antibodies and the antibiotic minocycline are being studied to see if they can stop the process of nerve destruction that follows injuries such as a blow to the head or stroke.

The findings will be difficult to substantiate because ALS is so rare, said ALS expert Martina Wiedau-Pazos of the University of California Los Angeles.

"We think there already are different forms of ALS," she said – potentially with different causes.

David Hovda, director of the UCLA Traumatic Brain Injury Research Center, said brain injury is very common with 1.5 million cases in the United States alone each year.

"Whether by itself in isolation it causes ALS, I do not think that this paper proves that. What I think it does is raise worries that individuals who had a career of exposure to repeat concussions … have a greater likelihood of developing motor neuron disease," he said.