Previous studies have suggested that blood could be a useful source of biomarkers for Alzheimer's disease.
The study, published in Translational Psychiatry, involved data from over 100 sets of twins - including 55 pairs of identical twins - allowing the researchers to demonstrate that any associations discovered between the blood protein and cognitive decline were independent of age and genetics.
Alzheimer's disease is an age-associated neurodegenerative disorder and the sixth leading cause of death in the USA.
According to the Alzheimer's Association, an estimated 5.3 million Americans of all ages have the condition. At present, no treatments are available to prevent the development of Alzheimer's disease.
Although the scientists are still searching for an effective treatment for Alzheimer's disease, what they do know is that prevention of the disease is likely to be more effective than trying to reverse it.
For a prevention trial to be effective, individuals at risk of the disease are required. Individuals at risk from Alzheimer's disease can be difficult to identify, however.
Although magnetic resonance imaging (MRI) and positron emission tomography (PET) brain scans can show visible signs of symptoms before symptoms are presented, these are expensive and require specialized facilities.
Many researchers are searching for surrogate markers that are relatively inexpensive and noninvasive yet provide enough information to benefit prevention trials, the authors write. For the new study, the team examined more than 1,000 proteins in the blood of 212 subjects (106 pairs of twins) using a protein biomarker discovery tool that measured a wide range of different proteins.
Each subject's cognitive ability was assessed using a computerized test known to be sensitive for detecting early Alzheimer's disease-related cognitive changes and the results of these were compared with the protein levels measured each individual's blood.
Further studies required to confirm protein's status as a biomarker
The researchers discovered that levels of one particular protein - MAPKAPK5 - was lower in the blood of individuals whose cognitive ability declined significantly over 10 years. MAPKAPK5 levels appeared to be associated with cognitive change in both the context of individuals and within pairs of twins.
It is the first time that MAPKAPK5 has been implicated in the development of Alzheimer's disease, having previously been studied in the context of cancer and rheumatoid arthritis.
The next step will be to replicate our finding in an independent study, and to confirm whether or not it is specific for Alzheimer's disease, as this could lead to the development of a reliable blood test, which would help clinicians identify suitable people for prevention trials.
If the research team can confirm the protein's status as a biomarker for modifiable cognitive aging, it would be of huge benefit to other researchers aiming to recruit at-risk asymptomatic individuals into prevention trials.
The researchers are very optimistic that our research has the potential to benefit the lives of those who don't currently have symptoms of Alzheimer's, but are at risk of developing the disease.
Funding for the UK-based study was provided by the Medical Research Council (MRC), the National Institute of Health Research Biomedical Research Centre for Mental Health and the Wellcome Trust.
References:
1. Plasma protein biomarkers of Alzheimer’s disease endophenotypes in asymptomatic older twins: early cognitive decline and regional bran volumes, Steven Kiddle et al., Translational Psychiatry, doi:10.1038/tp.2015.78, published online 16 June 2015, abstract.
2. MRC news release, accessed 16 June 2015.
3. Additional source: Alzheimer's Association, 2015 Alzheimer's disease facts and figures, accessed 16 June 2015.
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