GLOSSARY

Understanding the language of Alzheimer’s disease and emerging treatments

Medical discussions about memory, diagnosis, and new therapies often include unfamiliar terms. This glossary explains common words you may encounter along the way, including what they mean, how they are used, and why they matter in understanding Alzheimer’s disease and its treatment.

The cleanest way to organize your glossary is to separate:

  1. Biological substances in the brain (proteins / pathology)

  2. Measurements of those substances (biomarkers)

  3. Tests used to measure them

Think of it like this:

Protein → Biomarker measurement → Test used to measure it

Example:

Amyloid-beta protein → Aβ42/40 ratio biomarker → blood test or CSF test

If you structure your page that way, everything becomes much clearer.

1. Biological Proteins (What exists in the brain)

These belong under your Amyloid or Tau sections because they describe the actual molecules involved in the disease.

Amyloid section

  • Amyloid-beta (Aβ)
    The protein itself.

  • Aβ42
    A specific form of amyloid-beta.

  • Aβ40
    Another form of amyloid-beta.

These are proteins, not biomarkers by themselves.

They only become biomarkers when we measure them in blood or CSF.

Tau section

  • Tau protein
    The normal neuronal protein.

  • Phosphorylated tau (pTau)
    Abnormal tau associated with Alzheimer’s disease.

  • pTau217

  • pTau181

These are specific forms of tau protein that are strongly linked to Alzheimer’s pathology.

Again, they become biomarkers when we measure them in blood or CSF.

So you were absolutely right:

✔ pTau217 and pTau181 belong under “Tau and Neurofibrillary Tangles.”

2. Biomarkers (Measurements of proteins)

These belong in your Testing / Biomarker section.

A biomarker is not the protein itself — it is a measurement that tells us something about the disease process.

Example biomarkers

  • Aβ42/40 ratio
    A measurement comparing two amyloid proteins.

  • pTau217 level
    A measurement of phosphorylated tau.

  • pTau181 level

These can be measured in:

  • blood

  • cerebrospinal fluid

  • sometimes indirectly through imaging

3. Test Results / Diagnostic Conclusions

These are interpretations of biomarker measurements.

Example:

  • Amyloid positivity

This means testing (PET, CSF, or sometimes blood biomarkers) suggests amyloid plaques are present in the brain.

So this belongs in your diagnostic / interpretation section.

Where your listed terms should go

Amyloid and Amyloid-Beta section

  • Amyloid-beta (Aβ)

  • Aβ42

  • Aβ40

Tau and Neurofibrillary Tangles section

  • Tau protein

  • Phosphorylated tau (pTau)

  • pTau217

  • pTau181

Blood Biomarkers section

  • Aβ42/40 ratio

  • pTau217 (measured in blood)

  • pTau181 (measured in blood)

Important nuance:

Here you explain these are proteins measured in blood tests, not new molecules.

Diagnostic Interpretation section

  • Amyloid positivity

The easiest sentence to remember

Proteins cause the disease.
Biomarkers measure the proteins.
Tests detect the biomarkers.

Example for your site (this works beautifully)

Under Tau and Neurofibrillary Tangles

pTau217
A form of phosphorylated tau protein associated with Alzheimer’s disease. Levels of this protein can be measured in blood or cerebrospinal fluid and used as a biomarker for Alzheimer’s pathology.

Then under Blood Biomarkers

pTau217 blood test
A blood test that measures levels of phosphorylated tau protein to help identify Alzheimer’s disease.

One important clarification

There are three major types of Alzheimer’s biomarkers:

1. Amyloid biomarkers

Aβ42
Aβ40
Aβ42/40 ratio

2. Tau biomarkers

pTau217
pTau181

3. Neurodegeneration biomarkers

Neurofilament light chain (NfL)
Brain atrophy on MRI

This framework is called the ATN system in Alzheimer’s research.

If you'd like, I can also show you a very elegant 5-section glossary structure used by major Alzheimer’s centers that will make your page feel extremely organized and authoritative.

  • Changes that can appear on MRI scans during treatment with anti-amyloid therapies.

    ARIA-E: A form of ARIA involving temporary swelling or fluid accumulation in the brain (edema).

    ARIA-H: A form of ARIA involving small areas of bleeding in the brain (hemorrhage).

  • Lecanemab: the generic (or proper) name
    Leqembi: the brand name developed by Eisai and Biogen

    Medical definition: A recombinant humanized immunoglobulin gamma I (IgG1) anti-amyloid monoclonal antibody that binds to amyloid oligomers, protofibrils, and insoluble fibrils.

    Monoclonal Antibody: a laboratory-engineered protein designed to recognize and bind to a specific target in the body.

    Anti-Amyloid Therapy: a class of medications that target amyloid proteins in the brain to slow the progression of Alzheimer’s disease.

    Disease-Modifying Therapy: a treatment designed to slow or alter the biological processes underlying a disease rather than only treating symptoms.

    What it means: A laboratory-designed antibody that attaches to different forms of amyloid proteins in the brain.

  • A gene involved in lipid metabolism that influences risk for Alzheimer’s disease.

    APOE4: a specific variant of the APOE gene associated with increased risk for Alzheimer’s disease and higher risk of ARIA during anti-amyloid therapy.

    APOE2:

    APOE3:

  • Tau Protein
    A protein normally involved in stabilizing structures within neurons. In Alzheimer’s disease, abnormal tau accumulates inside brain cells.

    Neurofibrillary Tangles
    Bundles of abnormal tau protein that form inside neurons and disrupt normal cell function.

  • Small clusters of amyloid-beta proteins that form before plaques develop. These soluble aggregates are believed to be particularly harmful to neurons and are one of the targets of some newer therapies.

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Amyloid and Amyloid-Beta

Understanding the proteins and measurements involved in Alzheimer’s disease

Amyloid refers to a group of proteins that can accumulate in the brain in Alzheimer’s disease. These proteins, particularly amyloid-beta, can cluster together and form deposits known as amyloid plaques, which are one of the hallmark biological changes associated with the disease.

Researchers and clinicians measure different forms of amyloid to help determine whether Alzheimer’s disease is present and whether treatments that target amyloid may be appropriate.

Here are some of the most commonly used terms related to amyloid.

Tau and Neurofibrillary Tangles

Understanding the protein changes inside brain cells in Alzheimer’s disease

Tau is a protein that normally helps support the internal structure of nerve cells. In Alzheimer’s disease, tau becomes abnormally modified and begins to accumulate inside neurons. Over time, these abnormal tau proteins form structures known as neurofibrillary tangles, which interfere with normal cell function and contribute to brain cell damage.

While amyloid plaques develop outside neurons, tau tangles form inside neurons. Both are considered hallmark biological features of Alzheimer’s disease and play an important role in how the disease progresses.

Here are some commonly used terms related to tau.

  • Amyloid-beta is a protein that is naturally produced in the brain. In Alzheimer’s disease, these proteins can accumulate and stick together, eventually forming plaques between brain cells.

  • Clusters of amyloid-beta proteins that build up in the brain. These plaques are one of the defining biological features of Alzheimer’s disease and are believed to play a role in damaging nerve cells.

  • Two common forms of amyloid-beta protein found in the brain and in body fluids such as blood and cerebrospinal fluid.

    Changes in the levels of these proteins can provide clues about whether amyloid plaques are developing in the brain.

  • A measurement comparing the levels of two forms of amyloid-beta protein (Aβ42 and Aβ40). This ratio is often used in blood or cerebrospinal fluid tests to help determine whether amyloid plaques are likely present in the brain.

    A lower ratio is generally associated with a higher likelihood of amyloid buildup.

  • A term used when testing confirms that amyloid plaques are present in the brain. This confirmation may come from an amyloid PET scan or from biomarker testing.

    Many newer Alzheimer’s treatments require confirmation of amyloid positivity before treatment can begin.

  • A general term referring to the total amount of amyloid present in the brain. This is often measured using specialized imaging tests.

  • A standardized way of measuring the amount of amyloid detected on PET scans. The centiloid scale allows researchers and clinicians to compare amyloid levels across different imaging studies.

  • Tau is a protein naturally found inside neurons that helps stabilize structures called microtubules, which support the cell’s internal transport system.

    In Alzheimer’s disease, tau proteins become chemically altered and begin to detach from these structures.

  • Phosphorylated tau refers to tau proteins that have undergone a chemical change known as phosphorylation. This altered form of tau is more likely to clump together and form tangles.

    Elevated levels of phosphorylated tau can be detected in blood or cerebrospinal fluid and are used as biomarkers for Alzheimer’s disease.

  • A specific form of phosphorylated tau that has become one of the most accurate blood biomarkers for Alzheimer’s disease. Elevated pTau217 levels are strongly associated with the presence of amyloid plaques and tau pathology in the brain.

  • Another form of phosphorylated tau that can be measured in blood or cerebrospinal fluid. Like pTau217, it is used as a biomarker associated with Alzheimer’s disease.

  • Twisted bundles of abnormal tau protein that accumulate inside neurons. These tangles disrupt the normal functioning of brain cells and eventually contribute to cell damage and loss.

    The spread of tau tangles through the brain is closely related to the progression of symptoms in Alzheimer’s disease.

  • A general term referring to abnormal tau protein changes that occur in Alzheimer’s disease and certain other neurodegenerative conditions.

Testing and Biomarkers

Terms related to how Alzheimer’s disease is detected and confirmed.

Brain Imaging and Diagnostic Testing

Several types of tests are used to help identify Alzheimer’s disease and monitor changes in the brain.

Blood Biomarkers are tests that measure proteins associated with Alzheimer’s disease. These tests are increasingly used as screening tools to help determine whether more specialized testing may be needed.

Blood Biomarkers

Proteins measured in blood tests used to help detect Alzheimer’s disease

These are tests or measurements, not the proteins themselves.

Terms here:

  • Plasma biomarkers

  • Blood biomarker testing

  • Aβ42/40 ratio

  • pTau217 blood test

  • pTau181 blood test

  • Neurofilament light chain (NfL)

Cerebrospinal fluid (CSF) testing measures proteins associated with Alzheimer’s disease and can help confirm the presence of amyloid and tau pathology.

Cerebrospinal Fluid Testing

Laboratory tests that measure Alzheimer’s proteins in spinal fluid

Terms:

  • Cerebrospinal fluid (CSF)

  • Lumbar puncture

  • CSF amyloid testing

  • CSF tau testing

  • CSF pTau217

  • CSF pTau181

  • CSF Aβ42

  • CSF Aβ40

These tests often provide strong evidence of Alzheimer’s pathology.

Brain Imaging and PET Scans: brain imaging allows doctors to visualize changes in the brain, including the presence of amyloid plaques or structural changes related to neurodegeneration.

These tools help clinicians determine whether Alzheimer’s disease is likely present and whether treatments that target amyloid may be appropriate.

Brain Imaging and PET Scans

Imaging techniques used to detect brain changes

Terms:

  • MRI (Magnetic Resonance Imaging)

  • Amyloid PET scan

  • Tau PET scan

  • Radiotracer

  • Centiloid scale

These visualize amyloid, tau, or structural brain changes.

  • Laboratory tests that measure proteins associated with Alzheimer’s disease using a blood sample.

    These tests are becoming increasingly important as screening tools to help determine whether more specialized testing may be needed.

  • CSF is the clear fluid surrounding the brain and spinal cord. A small sample can be collected through a procedure called a lumbar puncture and tested for proteins associated with Alzheimer’s disease.

    CSF testing can measure amyloid and tau proteins and help confirm the presence of Alzheimer’s pathology.

  • A specialized brain imaging test that uses a tracer to detect amyloid plaques in the brain.

    This test can help confirm whether amyloid is present and is often used to determine eligibility for certain Alzheimer’s treatments.

  • A type of brain imaging that allows doctors to visualize tau protein accumulation in the brain. Tau PET imaging is primarily used in research but is increasingly being studied for clinical use.

  • A brain imaging technique that produces detailed images of brain structure.

    MRI scans are used to evaluate brain health, rule out other causes of cognitive symptoms, and monitor for potential side effects during treatment with anti-amyloid therapies.