People with a family history of Alzheimer's disease often have clumps of a toxic protein in their brains even though they are perfectly healthy, say researchers.
They said the findings could lead to new ways to identify people most likely to develop Alzheimer's disease, when there is still time to do something about it.
"The hope is to one day be able to diagnose very clearly the Alzheimer's disease process before any symptoms occur, when the brain is still healthy. Then the treatments would have the best chance of success," said Lisa Mosconi of New York University Langone Medical Center, whose study appears in the Proceedings of the National Academy of Sciences.
The team wants to continue to follow the people in the study to see whether they develop dementia, and they want to replicate the findings in a much larger study.
Several teams have been working on better ways to detect early-stage Alzheimer's disease in hopes of developing drugs that can fight it before it causes too much damage.
Current treatments cannot reverse the course of Alzheimer's, a mind-robbing form of dementia that affects more than 26 million people globally.
Mosconi's team used an imaging technique called positron emission tomography, or PET, with a fluorescent dye called Pittsburgh Compound B that lights up clumps of a protein called beta amyloid that are a hallmark of Alzheimer's disease.
The team imaged the brains of 42 people with an average age of 65, all with healthy brain function. Of these, 14 people had mothers who had Alzheimer's; 14 had fathers with the disease; and 14 had parents with healthy brain function.
Brain scans of all 42 showed that those whose parents — either fathers or mothers — had Alzheimer's were more likely to have amyloid plaques in their brains.
This was especially true of people whose mothers had Alzheimer's.
"They have pretty much 20 percent more amyloid beta deposits in their brains. In other words, they had an almost four times greater risk for amyloid beta pathology," Mosconi said in a telephone interview.
The finding confirms other studies that suggest having a mother with Alzheimer's may be a greater risk factor.
"It looks like if you have maternal history of Alzheimer's disease, the risk of amyloid beta plaque and a reduction in brain activity is much greater as compared to having a father affected," Mosconi said.
After advanced age, a family history of Alzheimer's is the single biggest risk factor for developing the disease.
Not everyone who has beta amyloid plaques in their brain develops Alzheimer's disease, but Mosconi said having the plaques does increase the risk.
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