The movie "Concussion" tells the story of the contentious dealings between the National Football League and forensic pathologist Bennet Omalu, MD, MPH, who identified a degenerative brain condition in football players now called chronic traumatic encephalopathy or CTE.

Omalu brought attention to the disease, which develops in pro athletes and others with a history of repetitive brain trauma. The NFL has faced mounting criticism in recent years that it is not doing enough to protect players from the head injuries that experts say can lead to CTE. It contends it is taking the issue seriously and making football safer.

Politics aside, the movie is bound to raise more awareness about the condition, for which even amateur athletes may be at risk, according to new research from Mayo Clinic. In the study, researchers looked at the brains of 66 men who had played contact sports in their youth. They found evidence of CTE in 21 of the brains, or 32 percent.

Related: Getting Ahead of Concussions

What we know about CTE

"We have known for a long time there is damage to the brain as a result of repetitive head trauma," says Brent Masel, MD, national medical director of the Brain Injury Association of America and president of the Transitional Learning Center at Galveston, a brain injury rehabilitation facility. "We used to call it dementia pugilistica." Boxers were once thought the be the primary victims, but not so anymore, says Masel. Here's what experts know.

What the symptoms are. Symptoms of CTE may include memory loss, impaired judgment, impulse control problems, depression, confusion and anxiety, among others, according to the CTE Center at Boston University. These symptoms start years or even decades after the brain trauma.

How it can (and can't) be diagnosed. People with CTE do show symptoms, but currently, no imaging method, such as MRI or CT, can diagnose CTE. The disorder can be definitively diagnosed only through an autopsy, says Masel. An autopsy can reveal telltale signs, such as the presence of a brain protein known as tau.

The likely causes. Experts believe it is the accumulation of repetitive brain injuries that leads to CTE, Masel says. These injuries include not only bad head bangs that cause a concussion, but also less severe injuries called sub-concussions, he says.

It's not caused by one bad incident. "One blow to the head is not the beginning of CTE," Masel says.

Related: Concussions Are Biggest Health Risk to Cheerleaders

How it differs from Alzheimer's disease. CTE and Alzheimer's disease have some similarities, but also differences. CTE symptoms generally present in people in their forties; Alzheimer's symptoms appear much later. Alzheimer's usually involve memory loss or these other, lesser-known Alzheimer's symptoms. People with CTE first show problems with judgment, reasoning, problem solving and impulse control, and they can display aggressive behavior, according to the CTE Center.

Advice for parents

In recent years, Masel says, as body weights have increased in the United States, blows sustained during contact sports have become more severe. And it's not just football games that pose a risk. Recent finds most concussions among high school and college football players happen during practice.

Football players aren't the only ones at risk of head injury, he says. Concussions occur in other sports, including soccer and cheerleading.

Parents must weigh the pros and cons to make contact sports as safe as possible for their children, Masel says. He suggests asking these questions if your child wants to play one:

  • Does the trainer have expertise in recognizing concussions?
  • Does the school have a protocol in place for what to do if a child suffers a concussion?
  • Do the school officials encourage return to school before return to play, showing their priorities are right?
  • Do the school officials understand the need for adequate recovery time, guided by input from the child's doctor?

It also pays to know the symptoms of a concussion. People mistakenly think a concussion always involved being ''knocked out," Masel says. Not so. While some people who suffer concussion are knocked out, others have what he calls altered awareness. They could report having blurred or double vision, seeing ''stars," being sensitive to light or noise, having a headache or feeling dizzy and having fatigue, nausea and vomiting.

Research about the best way to recover from concussions is still evolving, Masel says. "Right now we are not sure what the best approach should be." Some experts recommend absolute rest; others encourage reasonable activity. Masel tells people who suffer a concussion to rest for a few days. They don't need to be immobile in a dark room, he says, but they should take it easy.

Related: Should You Let Your Son Play Football?

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.