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Sept. 8, 2008 -- High blood levels of a plaque peptide may predict Alzheimer's disease in elderly people.
The finding comes from a study of 1,125 people who were in their late 70s when their blood was first tested. Four and a half years later, 104 of them had Alzheimer's disease.
Those with the highest blood levels of A-beta 42, a major component of the plaque that clogs the brains of Alzheimer's patients, were far more likely to get Alzheimer's than were those with the lowest A-beta 42 levels.
"Compared with individuals with low A-beta 42 levels at baseline, those with high A-beta 42 levels had more than a threefold increased risk of developing Alzheimer's disease over an average of 4.5 years," conclude Columbia University researcher Nicole Schupf, PhD, DrPH, and colleagues.
Interestingly, just before study participants developed the first signs of Alzheimer's disease, their A-beta 42 blood levels suddenly dropped. This, the researchers suggest, is a sensitive sign that a person has recently developed Alzheimer's.
Different studies of plaque peptides in the blood have come up with different results. Timing may have everything to do with this, Schupf and colleagues suggest.
When tested well before symptoms appear, the study suggests, people on the road to Alzheimer's will have high levels of A-beta in their blood. But when they finally get Alzheimer's, A-beta 42 sticks in the brain -- and blood levels drop.
The study also shows that blood levels of a second plaque peptide, A-beta 40, are not higher in people who eventually develop Alzheimer's disease.
The researchers say more work is needed to detail the patterns of change in A-beta levels and to see whether these patterns differ in people with genetic and environmental risk factors for Alzheimer's.
Schupf and colleagues report their findings in the Sept. 16 issue of Proceedings of the National Academy of Sciences.