by Taeh A. Ward, Ph.D.
Alzheimer’s disease (AD) is the most common cause of dementia in older individuals. While the greatest risk for developing AD is advancing age itself, about 40 percent of patients with AD also have at least one first-degree relative with AD (i.e. parent, sibling, child). However, a family history of AD does not necessarily mean that you will develop AD.
A well-known genetic marker for Alzheimer’s disease is the ε4 allele of apolipoprotein E (APOE-4). Having a copy of this allele from each parent results in approximately 30-55 percent risk of developing mild cognitive impairment or dementia due to AD by age 85. While rare genetic variants can cause 95-100 percent likelihood of developing early onset familial AD (e.g. APP, PSEN1, PSEN2), the majority of patients have much lower risk and generally develop AD due to a combination of genetics, environment and lifestyle (e.g. cardiovascular disease).
Neuroimaging and Biomarkers
While Alzheimer’s disease can cause changes in the brain detectible by standard neuroimaging, this is often observed after the disease has progressed. Other neuroimaging such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) can detect AD-associated changes even before significant cognitive symptoms but are not 100 percent accurate in diagnosing AD. Testing of cerebrospinal fluid (CSF) may reveal biomarkers of AD including amyloid beta protein, tau protein and phospho-tau expression levels. While biomarkers may have high diagnostic accuracy in patients who already have some cognitive impairment, they are less accurate for those with low risk for developing AD.
Benefits and Drawbacks of Medical Testing for Alzheimer’s Disease
When a treatment for AD is found, research indicates that early treatment may be more effective. Therefore it is important to develop tests that can detect AD before patients have cognitive symptoms. However, until a cure or highly effective treatment becomes available, genetic and other early medical testing have both benefits and drawbacks.
For individuals at high risk for AD, earlier diagnosis through medical testing allows for planning (e.g. advanced directive, setting up support systems and coping strategies) to ensure the best care and quality of life in the future. However, being diagnosed with AD through medical testing before you have cognitive difficulties can negatively impact sense of self, evoke anxiety and could have legal or other implications (e.g. driving, ability to own a gun, employment, insurance).
Having better knowledge about your risk factors for AD and other causes of dementia may help identify lifestyle changes which lower the risk of dementia or slow down onset (e.g. certain foods and cardiovascular exercise help protect the brain). Neuropsychological testing for those who have cognitive difficulties may identify curable causes such as vitamin deficiencies or depression, help rule out or diagnosis AD and inform treatment and care planning. Current medications for AD are intended to temporarily improve memory difficulties or confusion if already prominent and do not stop or cure AD. Cognitive testing can help determine if you may benefit from memory-enhancing medication.
Even individuals at high risk for developing Alzheimer’s disease can demonstrate intact cognitive and functional abilities for years before symptoms start. Until there is a cure or highly effective medication for AD, undergoing early medical testing is a personal choice which should be considered carefully since the results can impact emotions, life choices and other factors.
Dr. Taeh Ward, a clinical neuropsychologist at Pinehurst Neuropsychology, can be reached at 910-420-8041 or by visiting pinehurstneuropsychology.com