Los Angeles ( CNN ) -- An insidious , microscopic protein that has been found in the brain tissue of professional football players after death may now be detectable in living people by scanning their brains . Researchers say they found tau protein in the brains of five living retired National Football League players with varying levels of cognitive and emotional problems . `` It 's definite , we found it , it 's there , '' said Dr. Julian Bailes , co-director of the NorthShore Neurological Institute in Evanston , Illinois , and co-author of a new study that identified the tau . `` It was there consistently and in all the right places . '' Using a scan called positron emission tomography , or PET -- typically used to measure nascent Alzheimer 's disease -- researchers injected the players with a radioactive marker that travels through the body , crosses the blood-brain barrier and latches on to tau . Then , the NFL retirees had their brains scanned . `` We found ( the tau ) in their brains , it lit up , '' said Dr. Gary Small , professor of psychiatry at the Semel Institute for Neuroscience and Human Behavior at UCLA and lead author of the study , published Tuesday in the American Journal of Geriatric Psychiatry . What was startling , said Small , was the specific pattern of the tau they found : `` It was identical to what 's seen in a condition called chronic traumatic encephalopathy , CTE , that has only been diagnosed at autopsy . '' CTE is the disease that most likely played a role in the deaths of former NFL players like Dave Duerson , Ray Easterling , Shane Dronett , and Junior Seau . What has stymied researchers for years is that tau can only be uncovered after death . Finding it in living players is considered by many researchers to be the `` holy grail '' of concussion research , according to Bailes . `` After a while it gets old and not so fulfilling to take the brain out when ( an athlete ) is dead , '' said Bailes , a neurosurgeon and director of the Brain Injury Research Institute , which focuses on the study of traumatic brain injuries and their prevention . `` At that point there is no solution , no answer . '' More cases of brain disease found in football players . The research provides the beginnings of an answer , according to Bailes and Small . But the study is tiny , and poses looming questions . `` This is a very exciting but preliminary study , '' said Robert Stern , co-founder of the Center for the Study of Traumatic Encephalopathy at the Boston University School of Medicine . `` The researchers did what so many of us have been wanting to do for the last couple of years . `` The problem is that the type of PET scan they used is really not specific to what we 're looking at with chronic traumatic encephalopathy . '' The marker used in the PET scan -- the one that binds to tau -- is called FDDNP . The problem with using that marker , said Stern , is that it is not specific enough . It binds not just to tau , but also to another protein called beta amyloid , which is commonly seen in Alzheimer 's disease patients . `` In CTE , only tau is found in abundance , '' said Stern , an Alzheimer 's expert . `` What researchers saw was parts of the brain lighting up and showing abnormal findings . ... But we do n't know if what is lighting up is tau alone , or beta amyloid , or both . '' It 's the location of the protein that is important , Small said . In Alzheimer 's disease , tau is typically found in the outer part of the brain , called the cortex . `` It 's different from Alzheimer 's , '' said Small , director of the UCLA Longevity Center , adding that he found tau in deeper structures of the brain . `` The patterns of the scans are identical to what 's seen at autopsy in other people ( with CTE ) , '' like Seau , Duerson and Easterling , he said . `` And we know at autopsy it 's primarily tau . '' When tau lodges into those deep brain structures -- for example , the amygdala , which is associated with rage and other emotions , or the hippocampus , a seat of memory -- it causes major disruptions to those areas . Questions linger about long-term impact of subtle hits to the head . That disruption may be related to depression , memory problems and suicidal behavior common in cases of CTE studied thus far -- not just in retired NFL players , but in athletes in other sports and members of the military . The hope among the study 's authors is that a diagnostic brain scan might one day detect burgeoning CTE in all sorts of people who suffer concussions . But the current study is drawing some skepticism , doubts that likely will not ebb until future research examines a larger study group . `` Sometimes I wish ( study authors ) would hang on and wait until they have a more meaningful sample size , '' said Kevin Guskiewicz , a concussion expert and director of the Center for the Study of Retired Athletes at the University of North Carolina at Chapel Hill . `` I think that then people would be less skeptical of the findings . '' Still , Guzkiewicz is encouraged by the study results . `` Unfortunately we tend to identify these ( CTE ) cases when they 're already on the slippery slope toward dementia and it 's too late to do anything , '' said Guskiewicz . `` I 'm all for trying to build on studies like this . '' Building on the research -- expanding the study population -- is what Small and Bailes are working on now . In the meantime , they are optimistic about their findings . `` Right now , the ( FDDNP ) PET scan is the only method that we know of that can measure tau protein in living people , '' said Small . `` It 's not the perfect holy grail ... but for now it seems to be showing us what we 're looking for . '' Football players more likely to develop neurodegenerative disease .
Researchers find a protein called tau in the brains of living retired NFL players . Its pattern is identical to that found in chronic traumatic encephalopathy cases . CTE can only be diagnosed after death . Comment: