Is a Blood Test to Diagnose Alzheimer’s on the Near Horizon?

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Despite the tremendous advances that have been made in the understanding of Alzheimer’s disease in recent years, scientists have yet to pinpoint a cause. The leading, albeit yet to be proven, theory is that Alzheimer’s disease occurs because of an accumulation of a protein in the brain called beta-amyloid and that this then leads to alterations in another protein, called tau. The ensuing deposition of tau in the brain leads to dysfunction of brain cells and a loss of connections among them, ultimately causing them to die.

Recent research suggests that a simple blood test to detect beta-amyloid in the brain will be available soon-if you consider the next five years or so to be soon. Right now, the only ways to identify beta-amyloid in the brain are with positron-emission tomography (PET) or by analyzing cerebrospinal fluid after a spinal tap. These technologies are expensive and impractical. But recently, researchers developed a test capable of detecting beta-amyloid fragments in the bloodstream and, based on those amounts, predicting levels of the biomarker in the brain.

The investigators evaluated the predictive accuracy of the blood test in 363 people in Japan and Australia by comparing their estimates of brain amyloid based on the blood test with results of two standard beta-amyloid tests. The three tests correlated highly with one another for all three groups of participants in the study: those who were cognitively normal, had mild cognitive impairment (MCI), or had Alzheimer’s disease.

Though it remains to be seen whether such a blood test could be useful in diagnosing Alzheimer’s, these findings, which were published online last year in the journal Nature, are significant because they show that looking in the blood can reveal some of what is happening in the brain. One possibility for the near future is that a relatively inexpensive and simple blood test could be used to screen large numbers of people, and then those with positive results could be given a more definitive test such as a PET scan or spinal tap.