Blood test for dementia claims are premature
"Simple blood test … could predict if you'll suffer dementia," the Daily Mail reports.
This study aimed to identify a genetic score that could be used to indicate an individual's biological age. Using muscle and tissue samples from young and old adults, they identified the set of genetic markers that could best differentiate between the young and old samples.
They further tested this "healthy ageing gene score" using other tissue samples, including blood of people with and without Alzheimer's disease. They found that the score was lower in those with Alzheimer's. Overall, this score is suggested as a marker for healthy ageing.
However, it is important to realise this study is in the early experimental stages and the score has so far only been tested in small groups of people with known disease status. It is not known how well it could predict future disease development.
There is also the issue of the psychological impact of being told you are of "older" biological age, or may have higher risk of dementia or other chronic diseases – especially if there is little you can do to prevent this.
For now, there are steps you can take to reduce your risk of dementia and other chronic diseases, such as living a healthier lifestyle. There is also the option of signing up for a clinical trial looking at ways of preventing dementia.
You can sign up to take part in trials on NHS Join Dementia Research.
Where did the story come from?
The study was carried out by researchers from King’s College London and published in the peer-reviewed scientific journal Genome Biology.
The study received various sources of financial support, including InnoMed (Innovative Medicines in Europe), XRGenomics Ltd, Alzheimer’s Research UK, and The John and Lucille van Geest Foundation. Some of the authors are shareholders or have financial connection with shareholders in XRGenomics Ltd.
The article is open-access, so is freely available online.
The study has received extensive UK media coverage, which is generally premature. The headlines could suggest that people can go to their GP and request a blood test to determine their age and risk of dementia, which is certainly not the case. This study is in the early stages and there would be many things to consider before suggesting this could be a screening test.
The papers largely ignored the issue of whether being told you had a biological age older than your years, or had higher risk of dementia, would be welcome news.
What kind of research was this?
This was a laboratory study which aimed to build an RNA signature using tissue samples from older adults that could indicate how they were ageing.
It is expected that genetic signatures could be used to predict health risks and likelihood of chronic diseases of ageing. As the researchers suggest, such tests could help people take preventative measures.
However, to date, such tests have showed little promise in practice, and have not offered any benefit compared to standard practice (for example, identifying people who may be at risk of having high blood pressure or high cholesterol).
RNA helps to build proteins from the genetic code contained in DNA, and has recently been studied in the biology of ageing. It is also found abundantly in blood cells, and some previous studies have found differences in the blood RNA taken from people with and without Alzheimer's disease.
This study aimed to further explore RNA as a marker of ageing, and of cognitive health in particular.
What did the research involve?
This study involved identifying an RNA model of healthy ageing using samples of muscle tissue. This model was later tested using RNA from blood samples to see if this could support previous research findings and be used as an indicator of cognitive health.
The researchers took muscle tissue samples from individuals aged 25 to 65 years old, who were all of good health. They then identified the set of RNA markers that were the most reliable for distinguishing between the young and old tissue samples.
This set of markers (150 of them) was then further tested using other samples of human muscle, skin and brain tissue. These results supported the accuracy of this RNA signature for distinguishing between young and old tissue, and supported this as a marker for healthy ageing.
This so-called "healthy ageing gene score" was then tested using muscle samples from 108 men of average age 70 taking part in the Uppsala Longitudinal Study of Adult Men birth cohort. This aimed to see whether the score was associated with, or influenced by, other health and lifestyle factors.
The researchers finally looked at how well the score indicated cognitive health. They first looked at post-mortem brain tissue samples, and then finally tested this using blood samples from 717 age-matched "cases" with Alzheimer's disease and healthy "controls" without.
What were the basic results?
The Uppsala cohort demonstrated that despite all subjects being of the same age, there was a wide variation in their gene scores. This showed that the "healthy ageing gene score" was distinct from biological age.
The score was not associated with conventional disease markers (e.g. blood pressure or cholesterol), or with lifestyle factors (e.g. physical activity levels). The researchers noted that higher gene score was associated with better kidney function 12 years later, and improved survival 20 years later.
When finally looking at the RNA from blood samples, they found the healthy controls had significantly higher gene scores than those with Alzheimer's disease.
How did the researchers interpret the results?
The researchers conclude: "We identify a novel and statistically robust multi-tissue RNA signature of human healthy ageing that can act as a diagnostic of future health, using only a blood sample".
They go on to say: "this RNA signature has great potential to assist research aimed at finding treatments for and/or management of Alzheimer's disease and other ageing-related conditions".
Conclusion
This study identified an RNA signature or gene score that could potentially be tested in blood or other tissue samples and indicate an individual’s biological age. Generally, a higher score could indicate "healthier ageing" while a lower score could possibly indicate the presence of, or risk for, any chronic disease, including dementia.
However, it is important to realise that the research is only in the early experimental stages. Though the study demonstrated that a higher score could indicate healthier ageing, drawing any further implications from this would be difficult.
For example, there are no score "cut-off" points identified that could distinguish between healthy and less-healthy at particular ages (e.g. a healthy score for 40, 50 or 60 year olds). Even if a score was lower and in the "less healthy" bracket, it is not certain what this would mean.
The score hasn't been demonstrated to be specific to any particular disease. The researchers found it was lower in the cohort of people with Alzheimer's, but a low score wouldn't necessarily mean a person had, or was at risk of, Alzheimer's or any form of cognitive impairment. It also wouldn't be able to identify specifically whether a person had, or was at risk of, any other form of chronic disease, such as heart or vascular disease, or diabetes.
Determining the potential value of any such test in clinical practice is hard – just having a score would be of little value by itself in terms of preventing, diagnosing or managing any disease. It would need to be seen whether any such test could offer any benefit compared with standard medical practice.
There would also be many other things to assess, including who would be given the test, what could be the risks of a "positive test" (for example, the psychological effects of being told you are of "old" age), and importantly whether anything effective could actually be done about it.
Overall, the study is of interest, but it is too soon to suggest to the general public that they could have a blood test to determine their age and risk of types of dementia such as Alzheimer's.
Ways you can reduce your dementia risk include stopping smoking, drinking alcohol in moderation and maintaining a healthy weight through diet and exercise. These steps should help keep your cholesterol and blood pressure at a healthy rate.
A good rule is that what is good for the heart is also good for the brain.
