The brains of 435 individuals, aged 50-89 and without symptoms, were imaged to measure biomarkers associated with the development of Alzheimer’s disease. By age 85, more than 90% of participants had one or more abnormalities.
The use of specific indicators of disease, known as biomarkers, is an accepted tool in the diagnosis of Alzheimer’s disease. Two of these biomarkers are amyloid and tau protein. Amyloid and tau, as they develop within the brain, form deposits that can be identified by a brain imaging procedure called a PET scan. Tau has been associated with neurodegeneration, a progressive loss of structure and function in the brain. Neurodegeneration is associated with disorders other than Alzheimer’s disease and changes can be seen on a magnetic resonance imaging (MRI) scan.
Clifford R Jack Jr. and his colleagues investigated the prevalence of Alzheimer’s biomarkers amyloid, tau and neurodegeneration in the brains of cognitively unimpaired adults. They set out to measure the presence of amyloid and tau in the brains of men and women between the ages of 50 and 89. In addition, the researchers determined if there were signs of neurodegeneration. Their results were published in Lancet Neurology
The goal of the study was to estimate the age-specific and gender-specific frequency with which amyloid was present (A+), tau was present (T+), and brain degeneration had occurred (N+). With these three variables, researchers had a total of eight different combinations to consider ranging from A-T-N, meaning no biomarkers were present, to A+T+N+ signifying that all three were present.
They found that the number of men and women with no amyloid, tau, or degeneration (A-T-N) declined from the age of 50 onwards, while the number of men and women who showed signs of tau and degeneration (A-T+N+) or amyloid, tau and degeneration (A+T+N+) increased continuously with age, with more than 90% of subjects having one or more biomarker abnormalities by the age of 85.
These results raise the question – how do the different combinations of amyloid and/or tau deposits in combination with neurodegenerative changes affect the long-term clinical and cognitive outcomes for these individuals? Following these men and women over the course of many years and eventually by examining their brains after death may offer insight.
Written By: Sean Manning, BA, DC, MC