Alzheimer’s is detectable in healthy people years before they even start to show symptoms, another study has found.
University of Glasgow researchers say a combination of structural changes in the brain and cognitive decline could highlight people who are most at risk.
They looked at around 32,000 healthy Britons predisposed to the disease.
Those most at risk from dementia had small changes in part of the brain called the hippocampus and scored lower on reasoning and attention tests.
Experts said the finding could lead to new treatments or methods to catch the disease earlier, which could prompt lifestyle changes and slow its progression.
It is not known why certain people develop Alzheimer’s, but family history, smoking and being overweight are all risk factors.
Dozens of studies over past decade have hinted the disease could be caught decades before symptoms are first noticed.
Researchers found that people who are healthy but at-risk of developing Alzheimer’s had small differences in their brain structure and cognitive tests, compared to those who are not at-risk of developing the disease
The disease is most common in over-65s and increases with age, affecting on in 14 people over 65 and one in six over-80s.
More than have a million Britons have the condition and the figure is expected to reach 1.6million by 2040.
Meanwhile, more than six million people in the US have Alzheimer’s, where rates are also expected to double in the next 20 years.
Hope for dementia and Parkinson’s as scientists find driving factor for most diseases affecting brain function
Scientists believe they’ve found the culprit behind nearly all neurological diseases, in a breakthrough that could offer hope to millions.
Dementia, Parkinson’s and many other brain disorders are caused by key cells called neurons dying over time.
Researchers have now found other brain cells – known as astrocytes – play a ‘critical role’ in their death.
The star-shaped cells usually help clear away toxic particles that build up in the brain naturally or after head trauma, and are supposed to nourish neurons.
But laboratory tests on mice show astrocytes also release toxic fatty acids to kill off damaged neurons, confirming a suspicion many neurologists have had for years.
Lead researcher Professor Shane Liddelow, of New York University, said: ‘Our findings show the toxic fatty acids produced by astrocytes play a critical role in brain cell death.’
He added that the results ‘provide a promising new target for treating, and perhaps even preventing, many neurodegenerative diseases’.
The latest study, published in the journal Neuropsychopharmacology, looked at 32,790 adults without dementia in the UK, whose health information was stored in the UK Biobank database. They had an average age of 64.
The database includes in-depth data about their health, lifestyle and results from cognitive tests.
Researchers used polygenic risk scoring (PRS) – a method used to estimate an individual’s genetic risk of developing a particular disease, based on millions of genetic markers.
People with a higher PRS score had small differences in their hippocampus – one of the first parts of the brain to be affected by Alzheimer’s.
They also had lower fluid intelligence – the ability to reason and solve new problems – and matrix completion, which is the ability to recognise patterns. The experts said the study is the largest of its kind.
Rachana Tank, a PHD student at the University of Glasgow and lead author on the study, said: ‘Our findings are novel because they show the effects of genetic risk may, to a certain extent, be apparent long before a clinical dementia diagnosis.
‘Although we cannot say for certain that these differences are early signs of dementia per se, it is important that we do further research in this area.’
Dr Donald Lyall, lecturer in public health at the university’s Institute of Health and Wellbeing and study co-author, said the findings could ‘greatly improve’ treatment plans in the future.
Early identification of the disease could significantly change how it is managed and enable interventions that prevent or delay onset of the disease, according to Professor Paul Morgan, an expert in medicine in biology at Cardiff University.
He said population screening could be carried out using PRS scoring.
Brain imaging – the normal way dementia is diagnosed – is expensive and cognition tests are labour-intensive, he added.
Fiona Carragher, director of research and influencing at Alzheimer’s Society said: ‘If we can accurately identify people at risk of developing Alzheimer’s disease later in life, it could be a real gamechanger.
‘Early detection of those at a higher risk has the potential to pave the way for new treatments in the future and help researchers understand what causes diseases like Alzheimer’s to develop.
‘The scale of this study is significant. It adds further evidence to the theory that some brain changes associated with Alzheimer’s disease can start many years before symptoms such as memory loss.’
However, she noted the research only looked at people from a white European background – so it still needs to be established that there is an association between genetic factors and changes to the brain for those in other ethnic communities.