TESTS THAT PREDICT ALZHEIMER’S DISEASE

Biomarker is an infrequently used term. I can’t recall ever using it in med school, residency, or during my forty years in practice. Recently, however, it has been applied often in reference to tests that either diagnose dementia of the Alzheimer’s type or predict it’s future development. Biomarkers, then, are “biological molecules found in blood, other bodily fluids, or tissues that are a sign of a normal or abnormal process, condition, or disease…..It’s everything from blood pressure to heart rate to basic metabolic studies and X-ray findings to complex pathology specimens or genetic blood tests.” Today, Biomarkers are commonplace. 

Some diseases, like Alzheimer’s, can only be diagnosed at autopsy after the person dies. Exhaustive research is ongoing into finding a test, or biomarker, which can diagnose Alzheimer’s while the patient is still alive. While it’s absolutely wonderful we have a method to predict Alzheimer’s, there is no treatment for Alzheimer’s that affects its clinical course. Once you diagnose it, there’s nothing doctors can be do for it. 

This is my fourth blog on biomarkers for Alzheimer’s disease. The three previous articles were:

     “Now a Blood Test Can Predict Alzheimer’s Disease”     

     “Is There a Test To Tell if Grandma is Getting Alzheimer’s”

     “A New Way to Diagnose Alzheimer’s Disease”

Two of the articles referred to the analysis of a patient’s spinal fluid looking for protein substances that are indicators of the presence, or future possibility, of Alzheimer’s disease. The third article shared information about a blood test that predicted the occurrence of Alzheimer’s disease 6 years before it becomes clinically manifest. The substance is a Tau protein called P53.

Now comes an article on what I assume is a new test used similarly to P53. It is P-tau181, a marker for neurodegeneration. When the brain ages, shrinks, or degenerates, levels of P-tau181 are elevated in the blood. It was theorized that high blood levels of P-tau181 might correlate with the changes seen on a specialized form of a Positron Emission Technology (PET) scan. PET scans show deposits of Amyloid-B in the brains of patients with Alzheimer’s disease. Comparing blood levels of P-tau181 with PET scan Amyloid-B deposits there was a positive correlation.  

At the beginning of the study, blood levels of P-tau181 were determined in cognitively unimpaired patients. Then 7 years later, specialized PET scans were done to look for amyloid-B and Tau deposits in the brain. From these studies it was determined that “Elevated levels of P-tau181 were associated with greater accumulation of B-Amyloid on specialized PET scans.” 

What this all means is an elevated level of P-Tau181 in the blood is an accurate predictor for the development of Alzheimer’s at a later date. What was not stated in the reference articles is if those people with Amyloid-B deposits actually had Alzheimer’s dementia. It must be assumed they did because of the conclusion reached by the study.

It appears that now we have another biomarker (test) that both predicts and confirms the presence of Alzheimer’s dementia. The authors state P-tau181 outperformed two other tests for accuracy and predictability. That’s good news. But before we get too excited, we need to develop a treatment that will actually halt or reverse the symptoms of Alzheimer’s. Up to now, that has only been a dream. 

References: https://ntk-institute.org/new-research-identifies-blood-biomarker-for-predicting-dementia-before-symptoms-develop-1.

McGrath, ER. Blood Phosphorylated Tau 181 as a Biomarker for amyloid Burden on Brain PET in Cognitively Healthy Adults. J Alz Dis 2022:1-10.