Suppose that Alzheimer's disease, like a bacterial or viral infection, inspires the immune system to take action and defend the body. If this is true, then there must be antigen proteins that are specific to the disease, which the body recognizes as foreign and which triggers the mustering of a defense. Could doctors catch a glimpse of that process and diagnose the disease earlier? That's the hope behind a study out this week in Cell, led by Thomas Kodadek. Many new efforts to speed up diagnosis of Alzheimer's are ongoing, with some, like Kodadek's, looking for a signal in the bloodstream. The problem is, scientists don't know what antigens are the signature of the disease, nor which antibodies the immune system raises to go after them. So they set a trap. On a slide, Kodadek's team assembled thousands of different shapes of peptoids—molecules that are slight variations of the peptide molecules found in our bodies—and exposed them to blood samples from people with Alzheimer's and without. The idea was, if particular peptoids bound only to antibodies from people with Alzheimer's and not to antibodies of people without, then those antibodies they snagged could be considered a signature of Alzheimer's in the bloodstream.
The researchers tested the peptoid slides on blood from six likely Alzheimer's patients, six similarly aged healthy people, and six patients with a different neurodegenerative condition, Parkinson's disease. They identified three peptoids that recognized antibodies from people suspected to have Alzheimer's. Tested against 16 different people with the condition, each peptoid proved more than 93 percent accurate at diagnosing Alzheimer's, meaning they missed only one Alzheimer's case out of 16. [Scientific American]
Kodadek says his team has now applied the test to about 300 people, but the research is still nascent.
Dr Simon Ridley, head of research at the Alzheimer's Research Trust, said: "This very early research poses a new way of testing blood to diagnose Alzheimer's, but much more research must be done. We need to know how accurate and sensitive the test is and it also needs to be trialled in larger and more diverse groups of people." [BBC News]
Ridley and others are right to be cautious, as studies that raise new hope for finding and combating Alzheimer's are easily over-hyped. The New York Times, for instance, got itself in trouble
in August for reporting that a new test was "100 percent accurate" in predicting who would get Alzheimer's; in fact, the test was "up to 100 percent accurate" in identifying a signature protein group
in people who already had the disease. It was a proof of concept, not a foolproof test. This study is similar: Kodadek and colleagues succeeded in this early study in correctly distinguishing Alzheimer's patients from others. But the test has not been used to catch people on their way to developing the disease. If these findings are correct, though, they could shake up what's known about Alzheimer's, according to Stanford's Tony Wyss-Coray, who also researches proteins in the bloodstream that could be connected to the condition.
Wyss-Coray says it is still an open question as to whether or not people with Alzheimer's produce antibodies that are specific to their condition. However, the small number of peptoids unique to those with the disease could point to a very specific immune response against an unknown disease molecule. "If true, that would most certainly change the current view of this disease." [Scientific American]
And it could help clear the path to new treatments, Kodadek says:
The study's lead author stressed that the true benefits of such a test for Alzheimer's patients won't really arise until scientists develop effective treatments against the disease. "It's unclear whether people would want to know a couple of years ahead of time they are going to get Alzheimer's if they can't do anything about it," [he says]. "But I can say with some certainty that we will never get a good therapy for Alzheimer's without early diagnosis." [Healthday News]
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