Researchers have only recently been able to use brain scans to detect Alzheimer's risk factors in living people. iStockphoto hide caption

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The brain of former NFL star Junior Seau, who committed suicide last year, showed signs of the kind of neurodegenerative disease associated with repetitive head trauma. Elsa/Getty Images hide caption

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Junior Seau, seen here playing for the New England Patriots toward the end of his career, suffered from a degenerative brain disease, scientists say. Otto Greule Jr./Getty Images hide caption

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