dr. ann mckee.he's examined nearly 100 athletes' brains, and in a frightening number of cases she has found unnatural protein deposits. those are the same types of proteins found in alzheimer's patients. >> what we're seeing here, is this definitely caused by blows to the head? >> it's never been seen in any reported case except in a case of repeated blows to the head. the youngest case, to date, is a 17-year-old. >> the brain of nathan stiles? >> which is nathan stiles, right. ♪ >> hi. >> hello. >> welcome. chris n owinski. >> this is the stiles' first visit to the brain bank. >> what we've learned in the last three years is that it's a progressive disease, and then as the individual ages, if they're susceptible to this disease, it really becomes a widespread disease affecting large regions of the brain. >> so all of this was because of a concussion? >> probably more than one concussion. probably some concussive hits too. >> no one believed there was a problem until they were able to show -- >> unt

that's amazing. 17 years old. >> 17. >> and for the first time, dr. mckee is about to show nathan's parents what she found. >> hi. ann mckee. how do you do? >> nice to meet you. >> nothing ann mckee is about to tell them will bring nathan back. >> this is looking at it under the microscope and seeing all that dark brown. >> but the stiles hope this rare gift will tell us more about brain conditions than ever before. >> we have all the confidence that there's something to be learned from it. >> i think i want it to be my life's mission to make sure this doesn't happen to other kids. >> mckee knows how much more vulnerable these young kids may be. when the young developing brain is hit during football, no matter how hard, the brain is rocked. it's like an egg inside a shell. it stretches, the delicate fibers pulled, fluids violently sloshed around the brain, trying to absorb the blow. >> youth are at risk for any changes in that fluid balance, and they may not be able to handle it as well. >> sounds like you're saying they're more at risk than adults. >> oh,

. >> what was that like, to sit there and talk to dr. mckee? >> it's my son.o see the pictures of his brain, that's -- >> it's a lot. >> yeah. it's a lot. something you don't wish on your worst enemy. >> i think the good thing is you can see every effort is being made to learn from it. i think nathan is helping to come up with a plan to maybe what to do with concussions. >> you can see more about this in the documentary i put together. it's about a teen in north carolina trying to turn tragedy into triumph. can you play a safer game and still win? it's called "big hits, broken dreams" sunday, january 29th here on cnn. >>> football from another angle. danny, a rifle arm quarterback who won the heisman trophy, led the florida gators to the championship in 1996. later, he started a ministry. last year, he was hit by a rare disorder that literally knocked him off his feet. for danny, 1996 was a great year. he won the heisman trophy and led his team to the championship. deeply religious. he took his job as a role model seriously. >> when i was drafted to play with

dr. ann mckee runs the world's largest brain bank. her several years ago when she began finding evidence in the brains of deceased nfl players of unnatural protein deposits. those are the same kind of proteins found in alzheimer's. these symptoms are usually found in people in their 80s. is this definitely caused by blows to the head? >> it's never been seen in any reported case except for the case of blows to the head. >> reporter: that's exactly what the styles wanted to know when they phone natudonated nathan's. we saw telltale signs of the protein. does this surprise you? >> reporter: yes, it does, and it can start very early. >> hi, ann mckee, how do you do? >> reporter: nothing ann mckee will tell them can bring nathan back. but the styles hope that this rare gift will teach us more about brain concussions than we have ever known before. >> we have all the confidence in the world that there's something to be learned from it. >> i think it want it to be my life's mission to make sure that this doesn't happen to other kids. >> rep

dr. ann mckee runs the world's largest brain bank.tween the veterans administration and boston university. i first met her several years ago when she began finding evidence in the brains of deceased nfl players of unnatural protein deposits. those are the same kinds of proteins found in alzheimer's patients. it's a progressive degenerative disease which leads to dementia and alzheimer's-like symptom ps. but these symptoms are usually pound in people in their 80s, not their 40s. is this definitely caused by blows to the head? >> it's never been seen in any reported case except for the case of blows to the head. >> reporter: that's exactly what the styles wanted to know when they donated nathan's brain. did repeated blows to the brain cause that kind of damage in young nathan's brain? and the answer was yes. under the microscope -- >> that's really obvious. >> we saw tell-tale signs of the protein. did this surprise you? >> yes, it did. it can start very early. >> reporter: a's amazing. 17 years old. >> 17. >> reporter: and for the firs

dr. ann mckee runs the world's largest brain bank.joint project between the veterans administration and boston university. i first met her several years ago when she began finding evidence in the brains of deceased nfl players of unnatural protein deposits. those are the same kinds of proteins found in alzheimer's patients. it's a progressive degenerative disease which leads to dementia and alzheimer's-like symptom ps. but these symptoms are usually pound in people in their 80s, not their 40s. is this definitely caused by blows to the head? >> it's never been seen in any reported case except for the case of blows to the head. >> reporter: that's exactly what the styles wanted to know when they donated nathan's brain. did repeated blows to the brain cause that kind of damage in young nathan's brain? and the answer was yes. under the microscope -- >> that's really obvious. >> we saw tell-tale signs of the protein. did this surprise you? >> yes, it did. it can start very early. >> reporter: a's amazing. 17 years old. >> 17. >> reporter: