Scientists have taken a step closer towards developing a blood test for Alzheimer's disease.

In the largest study of its kind to date, scientists in the UK analysed blood samples from over 1,100 individuals, including people with Alzheimer's disease, people with mild cognitive impairment (MCI) and people with no signs of dementia.

MCI is a stage between normal cognitive ageing and dementia. Those with MCI have an increased risk of going on to develop dementia, including Alzheimer's disease. In fact, around 10% of people with MCI develop dementia within one year, however there is currently no accurate way of telling which people with MCI will go on to develop dementia.

The blood samples were analysed for 25 specific proteins that have previously been linked with Alzheimer's. Almost 500 of the participants from all three groups also had an MRI brain scan.

The scientists were able to identify 16 of the 26 proteins as being strongly linked with brain shrinkage in both Alzheimer's and MCI. They then carried out a second round of tests to determine which of these proteins could predict the progression from MCI to Alzheimer's.

They were able to identify 10 proteins that could predict whether people with MCI would go on to develop Alzheimer's within the next 12 months, with an accuracy of 87%.

Commenting on the findings, the study's lead author, Dr Abdul Hye of King's College London, pointed out that while memory problems can be common, ‘the challenge is identifying who is likely to develop dementia'.

"There are thousands of proteins in the blood, and this study is the culmination of many years' work identifying which ones are clinically relevant. We now have a set of 10 proteins that can predict whether someone with early symptoms of memory loss, or mild cognitive impairment, will develop Alzheimer's disease within a year, with a high level of accuracy," he said.

Also commenting on the findings, the study's senior author, Prof Simon Lovestone of the University of Oxford, noted that Alzheimer's starts to affect the brain ‘many years before patients are diagnosed with the disease'.

"Many of our drug trials fail because by the time patients are given the drugs, the brain has already been too severely affected. A simple blood test could help us identify patients at a much earlier stage to take part in new trials and hopefully develop treatments which could prevent the progression of the disease," he said.

He added that the next step will be ‘to validate our findings in further sample sets, to see if we can improve accuracy and reduce the risk of misdiagnosis, and to develop a reliable test suitable to be used by doctors'.

Alzheimer's disease affects an estimated 44 million people worldwide and some 35,000 people in Ireland. As the world's population ages, prevalence of the disease is increasing, however there is currently no cure and just five drugs are approved for treatment.

US scientists recently warned that the number of potential new Alzheimer drugs currently being developed is ‘relatively small' and the rate of success of clinical trials in this area is ‘limited'. (See more here)

However, according to the study's co-author, Dr Ian Pike of Proteome Sciences, these findings represent ‘a major advance in the development of a simple blood test to identify the disease before clinical symptoms appear'.

"This is the window that will offer the best chance of successful treatment. Equally important, a blood test will be considerably easier and less expensive than using brain imaging or cerebrospinal spinal fluid," he added.

Details of these findings are published in the journal, Alzheimer's and Dementia.

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