Tau proteins might be associated with dementia (including Alzheimer’s disease) as well as mild cognitive impairment and cognitive decline. The current study found that higher levels of total tau in blood plasma were significantly associated with cognitive decline.
Dementia represents a broad category of neurological diseases that cause gradual cognitive decline over time. The most common and well-known type of dementia is Alzheimer’s disease.On the other hand, mild cognitive impairment is, as its name suggests,a minor syndrome compared with dementia and Alzheimer’s disease. Mild cognitive impairment involves cognitive decline beyond what is expected for the age of an individual, but is not a great enough decline to interfere with daily activities. Furthermore, it is thought of as a transitional stage between normal aging and dementia.
There are many potential causes of dementia, and one involves the presence of dysfunctional tau proteins. Tau proteins help support microtubules, which are important for maintaining the structure of a cell. Dementia is associated with tau proteins that become dysfunctional and create tangles in the brain. Multiple studies suggest that total tau levels can be measured in blood plasma. However, very few studies have examined whether total tau levels in blood plasma could be used as a marker or a risk factor for cognitive decline. In a recent study, Mielke and colleagues examined the association between plasma total tau level, cognitive decline, and the risk of mild cognitive impairment and dementia.
The study was comprised of 458 participants aged 56 to 95 from the Mayo Clinic Study of Aging. Participants were seen every 15 months, which included a physical examination (including a neurological exam), interview, and neuropsychological testing. This determined whether participants had cognitive impairment or not. If so, they were categorized into mild cognitive impairment, dementia, or Alzheimer’s disease based on published criteria. Blood was also collected to determine plasma total tau levels.
The authors published their results in JAMA Neurology. They found that higher levels of plasma total tau were associated with an increased risk of mild cognitive impairment and cognitive decline, but not dementia or Alzheimer’s disease. Among participants who initially showed no cognitive impairment, higher levels of plasma total tau were associated with an increased risk of mild cognitive impairment upon follow-up. However, among participants with mild cognitive impairment, higher levels of plasma total tau were not associated with an increased risk of dementia upon follow-up. Yet among all participants, regardless of cognitive status, higher levels of plasma total tau were associated with cognitive decline. This important study demonstrates for the first time that plasma total tau level may be a useful prognostic risk factor or biomarker for cognitive decline. Further research is required to fully understand the connection between plasma tau levels and cognitive decline.
Written by Liana Merrill, PhD
Reference: Mielke, M.M. et al. (2017). Association of Plasma Total Tau Level With Cognitive Decline and Risk of Mild Cognitive Impairment or Dementia in the Mayo Clinic Study on Aging. JAMA Neurology.