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Spinal Tap to Predict Alzheimer's?
Nov. 19, 2002 -- While the exact cause of Alzheimer's disease is unclear, many experts agree that it often results in changes in the levels of two specific proteins floating in the fluid that "buffers" the brain.
Several studies show that compared to others, Alzheimer's patients have higher levels of tau protein and lower levels of beta-amyloid 42 protein in their cerebrospinal fluid (CSF). These proteins, the theory goes, stagnate in these altered states and form plaques that damage brain cells, causing memory loss and other symptoms associated with the disease.
Now, German researchers say these same altered protein levels are found in some people with the earliest signs of memory loss that progress to AD -- suggesting a new way to predict who will likely develop Alzheimer's. Their research shows a significant portion of people with memory impairment later develop AD.
The study analyzed the CSF of 28 people with memory impairment at the beginning and the end of the 18-month study. Twelve patients developed dementia, 10 of whom had probable Alzheimer's dementia. The other 16 patients were diagnosed as having either stable or progressive, worsening memory impairment. The groups of 10 and 16 had high tau levels and low beta-amyloid levels in their CSF.
"The CSF biochemical marker profile typical for AD -- elevated tau and decreased beta-amyloid 42 levels -- may often be present at a predementia stage of the disease," the researchers write in the November issue of The Archives of Neurology. "Shifting the diagnostic threshold to the predementia stage is of paramount importance with respect to disease-modifying treatment strategies."
But what's important to some researchers isn't practical to others.
"I don't think that looking at CSF content for these protein concentrations will ever become a routine diagnostic procedure because it's pretty invasive -- you need to undergo a spinal tap," says Bill Thies, PhD, vice president of medical and scientific affairs for the Alzheimer's Association. "Besides, no one really knows what to do with the answers."
While some studies implicate the high-tau, low-amyloid combination, others suggest that elevated concentrations of both proteins cause plaques to form. "There still isn't complete agreement on how these compounds change during the course of the disease," Thies tells WebMD. "It appears there may be a change in their amounts depending on the disease state and where they are measured -- in the CSF or brain or blood. These levels can go up, go down, go up again...."
The protein levels can be measured in a specific blood test, which has been used since 1996 -- but it's primarily used to predict a genetic predisposition toward Alzheimer's, and isn't necessarily an accurate measure of who will likely develop the disease independent of family history.
Another problem in identifying who is a "probable" Alzheimer's patient-to-be: The very clinical trials that hope to provide those answers.
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