Researchers in Germany have identified a new blood test that may in future provide much earlier diagnosis of Alzheimer’s disease and other degenerative disorders.

The team, from Saarland University and Siemens Healthcare, describe their test in the open access journal Genome Biology. They found it could be used to discriminate between people with Alzheimer’s and healthy people without dementia.

Alzheimer’s disease, the most common form of dementia, can currently only be diagnosed with certainty at autopsy, so there is considerable interest in finding reliable, non-invasive biomarkers for diagnosis in living people.

Andreas Keller focused on microRNAs (miRNAs), working with colleagues from Siemens Healthcare, Saarland University at Homburg, and three other German universities, as well as The Scripps Research Institute, of La Jolla, California. The small non-coding RNA molecules are known to influence the way genes are expressed, and miRNAs can be found circulating in bodily fluids, including blood.

The team highlighted and tested a ‘signature’ panel of 12 miRNAs among 48 people with Alzheimer’s and 22 healthy controls and discovered different levels in the people with the dementia.

They then developed the tests in a larger cohort of 202 people, comprising not only people with Alzheimer’s disease alongside healthy controls, but also patients with other neurological and neurodegenerative disorders.

Here, the new test not only reliably distinguished people with Alzheimer’s from the controls with normal health but was also able to identify other conditions.

Useful biomarkers need to be accurate, sensitive (correctly identifying people with the disease) and specific (correctly filtering out people without the disease).

The new test scored highly on all three measures. It was:

  • 93% accurate
  • 95% sensitive
  • 92% specific.

However, the authors caution that while their blood test shows obvious promise, it still needs to be validated for clinical use, and may eventually work best when combined with other standard diagnostic tools, such as imaging.

Since people with other brain disorders can sometimes show Alzheimer’s-like symptoms, the team also looked for the miRNA signature in other patient groups. Interestingly, while the 12 miRNAs were chosen for their potential to separate Alzheimer’s disease from controls, the same signature was more than 95% accurate in distinguishing controls from people with various psychiatric disorders, such as schizophrenia, depression and bipolar conditions.

It was less accurate (around 82%) in distinguishing patients with other neurodegenerative disorders, such as mild cognitive impairment, Parkinson’s disease and multiple sclerosis, from controls.

The test was also able to discriminate between Alzheimer’s patients and those with other neurodegenerative disorders, with an accuracy of around 75%.

The authors believe accuracy in distinguishing Alzheimer’s disease from the wider range of neurodegenerative conditions might be improved by tweaking the miRNAs used in the test. They explained:

Since the 12-miRNA signature has been tailored to differentiate between Alzheimer’s disease and controls, other miRNAs may likely contribute to a signature that permits also a better differentiation between the other tested diseases and Alzheimer’s disease.”

The work at Saarland builds on previous studies highlighting the potential of miRNAs as blood-based biomarkers for many diseases, including numerous cancers. It also suggests that miRNAs could yield useful biomarkers for various brain disorders and sheds further light on the mechanisms underpinning Alzheimer’s disease.

Two of the miRNAs are known to be involved in amyloid precursor protein processing, which itself is involved in the formation of plaques, a classic hallmark of Alzheimer’s disease. Further, many of the miRNAs are believed to influence the growth and shape of neurons in the developing brain.