Alzheimer's disease is the most common form of dementia. A new study by researchers at Indiana University has suggested that the disease could be already at work in the brain while the actual memory loss symptoms appear years later. The research team showed that the best-known genetic variant linked to Alzheimer's disease may be promoting deposits of plaque in the brain long before any symptoms of the disease can be measured on tests.
The study focused on patients with 'significant memory concerns', defined as older adults who complained that they had mentally slipped in recent months or years, but when given standard cognition and memory tests they fell within normal ranges. People who fall in this category have been called the 'subjective cognitive decline' group by Alzheimer's researchers.
The study authors, led by Shannon L. Risacher and Andrew J. Saykin, analyzed data from nearly 600 Alzheimer's Disease Neuroimaging Initiative (ADNI) participants. They compared those with the APOE e4 gene variant to those with other forms of the gene.
In the 'significant memory concerns' group the researchers found evidence of Alzheimer's-like pathologies from several bio-markers among the APOE e4 carriers including- increased levels of amyloid plaque, the clumps of protein fragments commonly found in the brain tissue of Alzheimer's patients. In the cerebrospinal fluid (CSF), decreased levels of the protein precursor to the plaques, suggesting that the protein was being recruited to the brain as part of the plaque creation process. In the CSF, increased levels of tau, another protein associated with Alzheimer's disease.
However, the analysis did not find evidence of reduced levels of glucose metabolism nor atrophy of brain structures that are associated with later stages of Alzheimer's progression. Risacher said, "The study provides the foundation for further focused research among patients at risk of Alzheimer's earlier than in much other research."
The research is published in Alzheimer's and Dementia.