Alzheimer’s disease could be definitively diagnosed for the first time after scientists proved brain scans can pick up the condition in its earliest stages.
Currently the only way to determine whether Alzheimer’s is present is to look at the brain of a patient after death.
For patients who are still alive, doctors usually use special cognitive tests which monitor memory and everyday skills such as washing and dressing.
But now researchers at the University of California have proven that it is possible to spot the sticky amyloid plaques and tau protein tangles which cause the disease and pinpoint the moment that they trigger Alzheimer’s disease.
The US scientists were able to track the progressive stages of Alzheimer’s disease, even in adults who showed no symptoms. It means that people at risk from the condition – such as one in five of the population who carry the APOE gene variant– could be regularly screened.
And it could reassure people who are suffering mild memory problems that they do not have the disease.
The distribution of tau and amyloid plaques in the brain is known as ‘Braak staging’ because it was discovered by Heiko and Eva Braak who studied the brains of Alzheimer’s patients after death.
“Our study is the first to show the staging in people who are not only alive, but who have no signs of cognitive impairment,” said study principal investigator Dr William Jagust, a professor at UC Berkeley’s School of Public Health.
“This opens the door to the use of scans as a diagnostic and staging tool.”
There are currently 850,000 people living with dementia in Britain which is due to rise to one million by 2025 and two million by 2050. Although there are currently no drugs to treat the disease it is hoped that within as little as five years treatments may be available which can delay the onset. It is therefore crucial to be able to pick up the disease early enough for drugs to be effective.
The new brain imaging is carried out using positron emission tomography scanners which look at cellular-level changes in organs and tissue.
Current scans only look for a decrease in brain cells or check that symptoms are not caused by another condition, such as a brain tumour.
The new technology was tested on 53 adults, five of whom were young adults, 33 pensioners without any neurodegeneration and 15 who had suspected Alzheimer’s disease. The scientists were able to prove definitively which were clear, at risk and those who had the condition.
The findings also shed new light on how tau protein and amyloid plaques build up as the brain ages.
For many years, the accumulation of amyloid plaques was considered the main culprit in Alzheimer’s disease. But tau is now also known to be responsible. When tau protein gets tangled and twisted, its ability to support connections between brain cells becomes impaired.
Through the PET scans, the researchers confirmed that with advancing age, tau protein accumulates in the medial temporal lobe – home to the hippocampus and the memory center of the brain. However when the tau went beyond that area Alzheimer’s begins.
The scientists believe that both tau and amyloid work together to cause the disease.
“Amyloid may somehow facilitate the spread of tau, or tau may initiate the deposition of amyloid. We don’t know. We can’t answer that at this point,” added Dr Jagust.
“All I can say is that when amyloid starts to show up, we start to see tau in other parts of the brain, and that is when real problems begin. We think that may be the beginning of symptomatic Alzheimer’s disease.”
Dr Samuel Lockhart, of UC Berkeley’s Helen Wills Neuroscience Institute added: “It’s not that one is more important than the other. Our study suggests that they may work together in the progression of Alzheimer’s.”
“Tau is basically present in almost every aging brain,” said visiting scholar Dr Michael Schöll, of Sweden’s University of Gothenburg.
“Very few old people have no tau. In our case, it seems like the accumulation of tau in the medial temporal lobe was independent of amyloid and driven by age.”
Dr James Pickett, Head of Research at Alzheimer’s Society said: “We know it can take months, and sometimes years, for some people to get diagnosed with Alzheimer’s and so a definitive way to diagnose the disease would be a big leap forward. Currently, the only way to know for sure whether someone’s memory impairment is due to Alzheimer’s disease is to examine their brain tissue after death and look for damaged proteins.
“This new scan allows us to see tangles of a protein called tau – one of the hallmarks of Alzheimer’s disease – inside the brain,but so far it has only been tested in a small number of people. Only 15 people with Alzheimer’s disease were included in this study, some of whom were not typical of the majority of cases. This makes it difficult to determine how useful the scan could be to support diagnosis.
“This technology is in the early stages of development and while it is beginning to provide researchers with important data about how Alzheimer’s disease develops, it is still many years before we could expect to see the scan being used in the clinic.”
Dr Simon Ridley, Director of Research at Alzheimer’s Research UK, said that the new brain scan looked ‘promising.’
“One challenge for diagnosing and researching diseases like Alzheimer’s is that it’s hard to know exactly what’s happening inside the brain over time.
“One important question that still remains in Alzheimer’s research is exactly where and when amyloid and tau proteins start to build in the brain and how this leads to the symptoms that people experience. It’s promising to see brain scan research now looking at both amyloid and tau in the brain in living people.
“Further research using PET scans to study tau will provide greater insight into how it interacts with amyloid and contributes to the disease, and whether this information could translate to meaningful improvements in diagnosis or treatments in the clinic.”
Source: The research was published in the journal Neuron.