ALLENTOWN, Pa.  A brain autopsy of a University of Pennsylvania football player who killed himself in April has revealed the same trauma-induced disease found in more than 20 deceased National Football League players, raising questions of how young football players may be at risk for the disease.

Owen Thomas, a popular 6-foot-2, 240-pound junior lineman for Penn with no previous history of depression, hanged himself in his off-campus apartment after what friends and family have described as a sudden and uncharacteristic emotional collapse. Doctors at Boston University subsequently received permission from the family to examine Thomas’s brain tissue and discovered early stages of chronic traumatic encephalopathy, a disease linked to depression and impulse control primarily among N.F.L. players, two of whom also committed suicide in the last 10 years.

Doctors in the Boston University group and outside it cautioned that Thomas’s suicide should not be attributed solely or even primarily to the damage in his brain, given the prevalence of suicide among college students in general. But they said that a 21-year-old’s having developed the disease so early raised the possibility that it played a role in his death, and provided arresting new evidence that the brain damage found in N.F.L. veterans can afflict younger players.

Thomas never had a diagnosis of a concussion on or off the football field or even complained of a headache, his parents said, although they acknowledged he was the kind of player who might have ignored the symptoms to stay on the field. Because of this, several doctors said, his C.T.E.  whose only known cause is repetitive brain trauma  must have developed from concussions he dismissed or from the thousands of subconcussive collisions he withstood in his dozen years of football, most of them while his brain was developing.