McKee believes that the damage to Grange’s brain was at the core of his A.L.S.

“We think the precipitating factor in his case was most likely the trauma,” McKee said. “First of all, he was absurdly young when he developed this disease. And he had considerable evidence of this trauma-induced tauopathy, or C.T.E.”

In hindsight, Grange’s family said that he showed symptoms of C.T.E. beginning in high school. He struggled to balance a checkbook. He did not understand the repercussions of failing classes. He once left for Seattle to try out for a soccer team and returned to find he had been fired from his job waiting tables because he never asked for time off. Grange fought depression in the years leading to his diagnosis, his parents said.

When he died, the Granges received a call from Boston University, requesting his brain. Learning that their son had C.T.E. was painful, but it brought some semblance of relief and peace. Like the doctors, they cannot be sure that their son’s death was precipitated by soccer, but they wish they would have discouraged his habit of heading the ball.

“Every park you go by, kids are playing soccer,” Michele Grange said. “And they’re doing headers. And that really bothers me. When I see the little kids playing soccer, even my grandson, for one thing it reminds me of better days. But on the other, it makes you think of the consequences. And I hope that these kids and their parents are going to see to it that they take care of their heads.”