Signs of Alzheimer's in brains of healthy people who are genetically predisposed to the degenerative disease may appear up to two decades before they would ever get diagnosed.
A new study, published online Nov. 6 in The Lancet Neurology, found that young people with no mental decline who possessed the so-called presenilin 1 (PSEN1) gene -- which has been linked to early-onset Alzheimer's -- showed differences in their brain scans when compared to those who didn't have the gene.
Early-onset Alzheimer's is a form of dementia that affects people starting in their 40s and 50s, according to the Alzheimer's Association. It affects people at a younger age, with most people with Alzheimer's will start showing decline around the age of 65.
More than 200,000 people in the U.S. have the early form of the disease. Because doctors don't usually look for signs of Alzheimer's in young people, it can be hard to get a diagnosis and take quite some time.
Nick Fox, a professor of neurology at University College London, told the BBC that some of the patients he diagnoses have already lost a fifth of their brain before they come in.
For the study, researchers scanned the brains of 44 young adults between the ages of 18 to 26. Twenty of them tested positive for the PSEN 1 mutation, but had not shown any symptoms of Alzheimer's.
When comparing their scans to people without the mutation, researchers saw that the people who had the PSEN1 mutation had more activity in the hippocampus and parahippocampus areas of their brains and less grey matter -- a part of the central nervous system made up of brain cells, nerve connections and blood cells -- in certain brain regions.
In addition, those with the mutation showed more amyloid beta protein in their cerebrospinal fluid. A buildup of the protein creates amyloid brain plaque, which has been considered a marker of Alzheimer's disease.
"These findings suggest that brain changes begin many years before the clinical onset of Alzheimer's disease, and even before the onset of amyloid plaque deposition. They raise new questions about the earliest brain changes involved in the predisposition to Alzheimer's and the extent to which they could be targeted by future prevention therapies," study leader Dr. Eric Reiman, the executive director at the Banner Alzheimer's Institute in Pheonix, Arizona, said in a press release.
Alzheimer's symptoms include memory loss and decline in intellectual ability which worsens over time. Late-stage individuals of Alzheimer's may not be able to hold a conversation or connect with their environment. There is currently no cure for the disease.
Fox, who wrote an accompanying editorial, added that while he doesn't think this research will help with early diagnosis, it may be beneficial in other ways.
"The key thing this does is open up the window of early intervention before people take a clinical and cognitive hit," he said.