A Potential Blood Test for Diagnosis of Alzheimer’s Disease

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Researchers from Saarland University and Siemens Healthcare report that a new blood test can accurately discriminate between healthy people and patients with Alzheimer’s disease. It’s hoped the non-invasive and relatively cheap test could one day help with diagnosis. The research is published in the open access journal Genome Biology [2].

Alzheimer's disease


Alzheimer’s disease is the most common form of neurodegenerative illness leading to dementia, a serious loss of global cognitive ability beyond what might be expected from normal aging. And it’s prevalence is growing: the global burden of Alzheimer’s disease is predicted to affect 1 in every 85 people by 2050 [2].

Today, diagnosis of Alzheimer’s disease can only made with certainty after a patient has died at autopsy. Because of this, scientists are working to find reliable, early and non-invasive diagnostic biomarkers, which are biological indicators of disease.

microRNAs (miRNAs) — small non-coding RNA molecules that regulate the expression of genes, and which can be found circulating in bodily fluids including blood — have demonstrated their potential as non-invasive biomarkers from blood and serum for a variety of diseases. A 2011 study provided first evidence that miRNA expression changes in blood may be valuable biomarkers for Alzheimer’s disease [3].

Scientists used next-generation sequencing to screen the expression of all human miRNAs in blood from patients with Alzheimer’s disease and healthy controls. They detected known human miRNAs as well as novel miRNA candidates that have not been previously cataloged.

In total, 416 miRNAs were identified. They selected 12 miRNAs for analysis in a larger cohort of patients, comprised of healthy people and patients with Alzheimer’s disease, as well as patients with other illnesses of the central nervous system. The 12 miRNAs were found to reliably distinguish between healthy people and patients with Alzheimer’s disease, demonstrating high scores (over 90%) for measures of sensitivity, specificity and accuracy.

Sensitivity: the proportion of samples correctly identified as positive (i.e. true positives).
Specificity: the proportion of samples correctly identified as negative (i.e. true negatives).
Accuracy: the proportion of samples correctly identified as true (i.e. both true positives and true negatives).

Since patients with other brain disorders can show symptoms similar to Alzheimer’s disease, researchers looked for the miRNA signature in other patient groups, including mild cognitive impairment, which is thought to precede the development of Alzheimer’s disease, multiple sclerosis, Parkinson’s disease, major depression, bipolar disorder and schizophrenia.

The test was able to distinguish healthy controls from patients with a variety of psychological disorders, including schizophrenia and depression, as well as from patients with other neurodegenerative disorders, such as mild cognitive impairment and Parkinson’s disease, albeit with lower accuracy.

Although the test shows promise, the data were only evaluated on a small group of 215 patients and healthy controls, so additional work will be required to elucidate the applicability of this 12-miRNA signature as a potential diagnostic test for Alzheimer’s disease. The scientists suggest that it may eventually work best when combined with other diagnostic tools, such as imaging.

The study also provides some clues on the molecular basis for Alzheimer’s disease. Two of the miRNAs are known to be involved in amyloid precursor protein processing, which is involved in the formation of plaques, a classic hallmark of Alzheimer’s disease. And many of the miRNAs are associated with the growth and shape of neurons in the developing brain.

There is no current treatment to delay or halt the progression of Alzheimer’s disease. However, there are a number of things you can do to lower your risk of developing the disease in the first place [4]:

  • Watch your blood pressure, keep it down. Chronic high blood pressure is the largest single risk factor for Alzheimer’s disease
  • Keep your cholesterol and homocysteine levels down
  • Exercise regularly
  • Engage in social and intellectually stimulating activities

References

  1. Leidinger et al. A blood based 12-miRNA signature of Alzheimer disease patients. Genome Biol. 2013 Jul 29;14(7):R78. [Epub ahead of print]
    View abstract
  2. Brookmeyer et al. Forecasting the global burden of Alzheimer’s disease. Alzheimers Dement 2007, 3:186-191.
  3. Geekiyanage et al. Blood serum miRNA: non- invasive biomarkers for Alzheimer’s disease. Exp Neurol 2011, 235:491-496
  4. Genes, Lifestyles, and Crossword Puzzles: Can Alzheimer’s Disease be Prevented? U.S. Department of Health and Human Services. 2006 June.
About the Author

Walter Jessen is a senior writer for Highlight HEALTH Media.