Alzheimer's Association Report Highlights Use of Biomarkers

Pauline Anderson

March 10, 2017

The increasing use of biomarkers, such as β amyloid and tau, to diagnose Alzheimer's disease (AD) will likely lead to more accurate estimates of the true incidence and prevalence of the disease, concludes a new special report from the Alzheimer's Association (AA).

The report is included in the association's annual "2017 Alzheimer's Disease Facts and Figures" document.

AD biomarkers have the potential to facilitate earlier and more accurate diagnosis and treatment, according to the report, authored by Heather M. Snyder, PhD, senior director, medical & scientific operations, Alzheimer's Association, and colleagues.

"Many researchers believe that early intervention — either at the mild cognitive impairment (MCI) stage or even before symptoms start — offers the best chance of slowing or stopping the progression of Alzheimer's disease and therefore the best chance of preserving brain function," Dr Snyder told Medscape Medical News.

Current methods of diagnosing AD don't conform to what's known about the disease, the authors note. The 1984 criteria established by the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) and the Alzheimer's Disease and Related Disorders Association (ADRDA) defined AD as a clinical disease caused by underlying changes. The assumption was that patients with an amnestic dementia would have amyloid plaques and tau neurofibrillary tangles at autopsy and those without amnestic dementia would not.

However, studies since then have shown that clinical symptoms and underlying brain changes don't always align, the authors note. Autopsy studies showed 10% to 30% of people who met NINCDS-ADRDA criteria for AD did not have significant AD-related brain changes. And autopsy studies in people who were cognitively normal for their age showed about 30% had AD-related brain changes.

Biomarkers developed over the past 2 or so decades fit into two classes: (1) brain imaging of amyloid and tau accumulation and of brain volume and brain metabolism changes and (2) measures of relevant proteins in spinal fluid.

Both the National Institute on Aging (NIA) and the AA have proposed that, when used alongside clinical criteria, these biomarkers can increase the confidence that a diagnosis of dementia is or is not due to AD. The NIA-AA also proposed that biomarkers could identify MCI as due to AD or to other conditions.

Further, the NIA-AA suggested that cognitively healthy people with abnormal AD biomarkers have preclinical AD. If that's the case, individuals who have no cognitive impairment but have AD biomarkers will be determined to have AD.

A biomarker-based diagnosis of Alzheimer's disease — one based on brain changes, not cognitive or functional changes — will change the incidence and prevalence of Alzheimer's, but "exactly how that comes out at the end of the day is still an open question,'" said Dr Snyder.

What is known is that the new approach to diagnosis will remove a population currently included in the estimates (those with dementia but no AD biomarkers) but add a population not now included (those with AD biomarkers but no dementia).

This addition would include patients with MCI. It's estimated that up to 56% of those with MCI have AD biomarkers.

According to current criteria, the AD prevalence among those aged 65 years and older in 2017 is estimated to be 5.3 million. Two thirds of them are women.

Snyder. They enable researchers to identify which persons to enroll in clinical trials to test new therapies and further allow monitoring of the effects of those treatments.

And the field of biomarkers seems to be expanding. "We are seeing a number of different types of studies looking at more noninvasive, lower-cost, and more applicable approaches" to diagnosing dementia, said Dr Snyder.

She pointed to preliminary research showing that a simple saliva test may eventually help diagnose AD. The small study analyzed metabolites in saliva samples from those with normal cognition for their age, those with MCI, and those with AD, and it found patterns of metabolites in those with AD and MCI.

Additional research and development of guidelines for the future use of biomarkers is "urgently needed" to optimize therapeutic strategies for the potentially much larger population of people with AD, the report notes.

In the future, AD may no longer be viewed as a disease leading to irrevocable cognitive and functional decline and death but rather a chronic condition like cardiovascular disease, AIDS, or some cancers that might be optimally managed with early intervention, said Dr Snyder.

"Whether it's lifestyle modifications that are encouraged, like we do for heart disease, or it's medications that are provided, like we do for heart disease, the idea is that you are stopping or slowing the progression of the disease and the continued underlying biological changes."

The field "is not at that point yet," but that's where it's headed, said Dr Snyder.

High Cost for Payers, Families

Also reported in the new "Facts and Figures" document are annual payments for dementia care. For the first time, total payments exceeded a quarter trillion dollars ($259 billion). These payments include healthcare, long-term care, and hospice care but don't include lost work and other costs incurred by patients with dementia and their caregivers.

The document also includes new research on the physical and mental impact of AD on caregivers, including family members. This burden disproportionately affects women, who tend to spend more time caregiving than men.

More than 15 million Americans provide unpaid care in the form of physical, emotional, and financial support for patients with AD dementia. In 2016, AD caregivers provided an estimated 18.2 billion hours of unpaid care, a contribution valued at $230.1 billion.

Barring the development of a medical breakthrough, the number of people aged 65 years and older with AD may nearly triple to 13.8 million by 2050.

AD is the sixth leading cause of death in the United States and the fifth leading cause of death for those aged 65 and older. It's the only disease among the top 10 causes of death in the United States that can't be prevented, cured, or even slowed.

2017 Alzheimer's Disease Facts and Figures. Full text

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