Measuring people's changes in cognitive abilities is a better predictor of Alzheimer's disease than changes in biomarkers, researchers from the Benito Menni Complex Assistencial en Salut Mental, Barcelona, Spain, reported in Archives of General Psychiatry, a JAMA journal.
The authors explain that changes in cerebrospinal fluid levels of some proteins or alterations in brain volume are examples of biomarkers that have helped researchers better understand how Alzheimer's disease develops and progresses - these biomarkers have also helped them determine whether treatments are effective.
Cognitive changes, demographic variables and genetic risk factors - known as behavioral markers - are also linked to Alzheimer's disease.
However, the researchers say:
"Despite formidable evidence for the predictive validity of individual biomarkers and behavioral markers, they have rarely been examined in combined models."
Jesus J. Gomar, Ph.D. and team set out to find out how accurate cognitive markers and biomarkers are at predicting whether patients with Mild Cognitive Impairment (MCI) will develop Alzheimer's disease.
MCI or Mild Cognitive Impairment is in between the normal cognitive decline that comes with normal aging and the more severe decline that occurs with dementia. The individual with MCI has problems with thinking, judgment, language and memory, to a greater extent than would be typical at his/her age. However, the individual is still able to go about daily life and perform usual activities.
The researchers also wanted to determine whether any of these markers were linked to a disproportionate extent of decline.
They gathered data from ADNI (the Alzheimer's Disease Neuroimaging Initiative) database, which included 116 patients with MCI that went on to develop Alzheimer's disease within 24 months, 204 with MCI who did not develop Alzheimer's, and 197 healthy controls.
The investigators used a range of tests to assess the participants' cognition and how well they functioned. Cognition is the mental process of knowing, and includes perception, awareness, reasoning and judgment. They also took cerebrospinal fluid samples from them at the beginning of the study and every year for two years. Participants' blood samples were also taken when the study began - this was tested for genes which are linked to Alzheimer's disease. From MRI (magnetic resonance imaging) results included in the ADNI, they were able to gather data on the participants' cortical thickness and brain volume.
They found that cortical thickness of the left middle temporal lobe of the brain, as well as two measures of delayed memory in those with MCI were linked to a higher likelihood of developing Alzheimer's disease within 24 months.
Changes in functional activity scores seemed to show a greater rate of decline in the participants than changes in biomarkers.
Declines in the Functional Assessment Questionnaire and the Trail Making Test (part B) scores appeared to be good predictors of Alzheimer's disease risk within twelve months for participants with MCI.
The researchers wrote:
"Cognitive markers at baseline were more robust predictors of conversion than most biomarkers. Longitudinal analyses suggested that conversion appeared to be driven less by changes in the neurobiologic trajectory of the disease than by a sharp decline in functional ability and, to a lesser extent, by declines in executive function."
Ideally, one should use all available data to accurately predict conversion to Alzheimer's, the researchers added.
Written by Christian Nordqvist