Recent studies have identified biomarkers which can help predict the risk, as well as recognize the existence, of Alzheimer’s disease. Now, researchers involved with the National Institute on Aging (NIA) and the Alzheimer’s Association (AA) have proposed a new biomarker-based definition of Alzheimer’s disease.
An article published in the April 2018 journal Alzheimer’s & Dementia discusses the proposal that Alzheimer’s disease should be defined by measurable, underlying pathologic processes that are able to be documented by either biomarkers or autopsy. This definition would be used for observational and interventional research only and would not affect clinical care at this time.
This change shifts the emphasis of Alzheimer’s from a “syndrome” to a biological construct and also updates diagnostic guidelines the NIA and AA previously established for preclinical, mild cognitive impairment, and dementia stages of Alzheimer’s disease.
Dr. Clifford Jack, chair of the committee that created this paradigm, says that this change would add Alzheimer’s disease to the list of biomarker-defined disorders including, but not limited to, hypertension, diabetes, and hyperlipidemia. Because the disease would be defined biologically, patients involved in disease-modifying trials would undergo biomarker tests.
Dr. Jack goes on to say that, with the adoption of this new framework, the hope is that clinical trials will be “far more effective than they have been in the past and will enroll only people who actually have the disease they’re being treated for.”
Alzheimer’s disease has always been defined as a clinical syndrome, a progressive decline in cognitive abilities with a prominent memory component that eventually leads to loss of independence. In the past, it was termed “possible or probable Alzheimer’s disease,” and then just shortened to “Alzheimer’s disease.” Unfortunately dementia became equated with Alzheimer’s disease, which is misleading as many people labeled with Alzheimer’s did not have the signature amyloid plaques and tau tangles associated with the illness.
The new guidelines would take care of this confusion as Alzheimer’s disease would be defined by beta amyloid deposition and pathologic tau. A person with biomarker evidence of both amyloid beta and pathologic tau would be classified as having Alzheimer’s disease. A person with biomarker evidence of amyloid deposition and a normal pathologic tau biomarker would be labeled as having “Alzheimer’s pathologic change.” Alzheimer’s disease and Alzheimer’s pathologic change would be phases along the Alzheimer’s continuum, independent of clinical symptoms.
It is interesting to note that neurodegenerative biomarkers and cognitive symptoms, neither of which is specific to Alzheimer’s disease, would still be taken into consideration. However, they would only be used to indicate severity, not to define the presence of the Alzheimer’s continuum.
In a related article also published in Alzheimer’s and Dementia, James Hendrix, PhD, and his colleagues noted some difficulties in implementing the proposed guidelines in research. Obtaining biomarkers adds time and expense to studies and might involve both invasive procedures and exposure to radiation. In addition, PET imaging is not always widely outside of major medical centers, which could cause logistical issues.
But Dr. Hendrix goes on to say that the benefits might outweigh the costs, as this new framework could ensure that people involved in studies for Alzheimer’s disease actually have the disease. Obviously, this would greatly benefit further research into the mysteries of Alzheimer’s disease and hopefully lead to better drugs and/or therapy for this horrible disorder.