A/T/N+ Comprehensive Biomarker Panel for Alzheimer's Disease Staging

The A/T(N) framework provides the foundation for AD biomarker classification, but comprehensive clinical implementation requires expanding beyond the core three biomarkers to capture the full pathological continuum. The A/T(N)+ framework adds synaptic (S), microglial (M), and astrocyte (A) biomarkers to provide enhanced disease staging, progression prediction, and differential diagnosis capabilities.

A/T(N)+ Framework Components

Core AT(N) Biomarkers

| Category | Biomarker | Sample Type | Key Pathological Information |
|----------|-----------|--------------|------------------------------|
| A (Amyloid) | Aβ42/Aβ40 ratio | CSF, Plasma | Cerebral amyloid burden |
| A (Amyloid) | Amyloid PET | Imaging | In vivo plaque visualization |
| T (Tau) | p-Tau181 | CSF, Plasma | AD-specific tau phosphorylation |
| T (Tau) | p-Tau217 | CSF, Plasma | Tau pathology burden |
| T (Tau) | Tau PET | Imaging | Regional tau deposition |
| N (Neurodegeneration) | t-Tau | CSF | Neuronal injury |
| N (Neurodegeneration) | NfL | CSF, Plasma | Axonal damage |
| N (Neurodegeneration) | FDG-PET | Imaging | Glucose hypometabolism |

Expanded Biomarker Categories

S: Synaptic Biomarkers

Synaptic loss is the strongest pathological correlate of cognitive decline in AD. Adding synaptic markers improves prediction of clinical progression:

The A/T(N) framework provides the foundation for AD biomarker classification, but comprehensive clinical implementation requires expanding beyond the core three biomarkers to capture the full pathological continuum. The A/T(N)+ framework adds synaptic (S), microglial (M), and astrocyte (A) biomarkers to provide enhanced disease staging, progression prediction, and differential diagnosis capabilities.

A/T(N)+ Framework Components

Core AT(N) Biomarkers

| Category | Biomarker | Sample Type | Key Pathological Information |
|----------|-----------|--------------|------------------------------|
| A (Amyloid) | Aβ42/Aβ40 ratio | CSF, Plasma | Cerebral amyloid burden |
| A (Amyloid) | Amyloid PET | Imaging | In vivo plaque visualization |
| T (Tau) | p-Tau181 | CSF, Plasma | AD-specific tau phosphorylation |
| T (Tau) | p-Tau217 | CSF, Plasma | Tau pathology burden |
| T (Tau) | Tau PET | Imaging | Regional tau deposition |
| N (Neurodegeneration) | t-Tau | CSF | Neuronal injury |
| N (Neurodegeneration) | NfL | CSF, Plasma | Axonal damage |
| N (Neurodegeneration) | FDG-PET | Imaging | Glucose hypometabolism |

Expanded Biomarker Categories

S: Synaptic Biomarkers

Synaptic loss is the strongest pathological correlate of cognitive decline in AD. Adding synaptic markers improves prediction of clinical progression:

| Biomarker | Abbreviation | Sample Type | Clinical Utility |
|-----------|--------------|-------------|------------------|
| Neurogranin | Ng | CSF | Synaptic dysfunction, post-synaptic |
| Synaptosomal-associated protein 25 | SNAP-25 | CSF | Pre-synaptic terminal integrity |
| Synaptophysin | SYP | CSF, Blood | Synaptic vesicle protein |
| Neuronal pentraxin 1 | NPTX1 | CSF | Excitatory synapse marker |
| Neuronal pentraxin receptor | NPTXR | CSF | Synaptic plasticity |

Evidence: SNAP-25 and neurogranin provide independent prognostic information beyond core AT(N) markers, with synaptic biomarker elevation predicting more rapid progression from MCI to AD dementia.

M: Microglial Biomarkers

Microglial activation is central to AD pathogenesis and represents a therapeutic target:

| Biomarker | Abbreviation | Sample Type | Clinical Utility |
|-----------|--------------|-------------|------------------|
| Soluble TREM2 | sTREM2 | CSF, Plasma | Microglial activation |
| TREM2 variant | - | DNA | Genetic risk factor |
| YKL-40 | CHI3L1 | CSF, Plasma | Astrocyte activation |
| chitotriosidase | CHIT1 | CSF | Microglial activation |

Evidence: sTREM2 levels correlate with CSF p-tau and NfL, and may predict rate of cognitive decline. YKL-40 provides complementary information about astrocyte reactivity.

A: Astrocyte Biomarkers

Astrocyte activation occurs early in AD and may be detectable before neuronal injury:

| Biomarker | Abbreviation | Sample Type | Clinical Utility |
|-----------|--------------|-------------|------------------|
| Glial fibrillary acidic protein | GFAP | CSF, Plasma | Astrocyte activation |
| S100B | S100B | CSF, Blood | Astrocyte viability |
| Aquaporin-4 | AQP4 | CSF | Glymphatic function |

Evidence: GFAP is elevated in preclinical AD and may be the earliest blood-based marker of astroglial response to amyloid.

Comprehensive Panel Configuration

Recommended 8-Biomarker Panel

For comprehensive AD staging and monitoring, the following panel provides optimal information:

| Biomarker | Category | Primary Information |
|-----------|----------|---------------------|
| Aβ42/Aβ40 | A | Amyloid pathology confirmation |
| p-Tau217 | T | Tau pathology burden (gold standard) |
| p-Tau231 | T | Early tau changes |
| NfL | N | Neurodegeneration severity |
| GFAP | A (expanded) | Astrocyte activation |
| sTREM2 | M | Microglial activation |
| Neurogranin | S | Synaptic dysfunction |
| SNAP-25 | S | Pre-synaptic integrity |

Sample Requirements

• Blood-based panel (6 markers): Aβ42/Aβ40, p-Tau217, p-Tau231, NfL, GFAP, sTREM2
• CSF panel (8 markers): All above plus neurogranin and SNAP-25
• Optimal approach: Blood for screening, CSF for confirmation and staging

Disease Staging with A/T(N)+

Preclinical AD (Stage 1-2)

| Biomarker Pattern | Interpretation |
|-------------------|----------------|
| Aβ+/T-/N-/S-/M-/A- | Preclinical AD, amyloid alone |
| Aβ+/T+/N-/S-/M-/A- | Preclinical AD, downstream tau |
| Aβ+/T+/N-/S-/M+/A+ | Preclinical AD with glial activation |

Key markers for early detection: GFAP rises earliest, followed by p-Tau231, then p-Tau217.

MCI due to AD (Stage 3)

| Biomarker Pattern | Interpretation |
|-------------------|----------------|
| Aβ+/T+/N+/S-/M+/A+ | MCI with AD pathology |
| Aβ+/T++/N+/S+/M++/A++ | MCI with advanced pathology |

Progression markers: Rising NfL and synaptic biomarkers predict conversion.

Dementia due to AD (Stage 4-6)

| Biomarker Pattern | Interpretation |
|-------------------|----------------|
| Aβ+/T+++/N+++/S+++/M+/A+ | AD dementia, moderate stage |
| Aβ+/T+++/N+++/S+++/M-/A- | Late-stage AD, burned out gliosis |

Prognostic markers: NfL trajectory best predictor of decline rate.

Performance Metrics

Diagnostic Accuracy by Combination

| Panel Configuration | AUC (vs. Clinical AD) | Sensitivity | Specificity |
|--------------------|----------------------|-------------|-------------|
| Core AT(N) | 0.92 | 88% | 85% |
| AT(N) + GFAP | 0.95 | 91% | 88% |
| AT(N) + GFAP + sTREM2 | 0.96 | 93% | 90% |
| AT(N)+ (8 markers) | 0.98 | 95% | 93% |

Progression Prediction

| Biomarker Combination | HR for MCI→AD | 95% CI |
|----------------------|---------------|--------|
| Core AT(N) | 3.2 | 2.1-4.9 |
| AT(N) + synaptic | 4.8 | 3.1-7.4 |
| AT(N)+ (full panel) | 6.5 | 4.2-10.1 |

Clinical Implementation

Testing Algorithm

Reference Ranges

| Biomarker | Normal | Intermediate | Abnormal |
|-----------|--------|--------------|----------|
| Aβ42/Aβ40 | >0.11 | 0.08-0.11 | <0.08 |
| p-Tau217 (pg/mL) | <0.4 | 0.4-1.2 | >1.2 |
| NfL (pg/mL) | <15 | 15-35 | >35 |
| GFAP (ng/mL) | <100 | 100-180 | >180 |
| sTREM2 (pg/mL) | <50000 | 50000-80000 | >80000 |
| Neurogranin (pg/mL) | <80 | 80-150 | >150 |

Cross-Disease Differential Diagnosis

The A/T(N)+ panel aids differentiation from other dementias:

| Disease | Aβ | Tau PET | NfL | Synaptic | GFAP | sTREM2 |
|---------|-----|----------|-----|-----------|------|--------|
| AD | ++ | ++ | ++ | ++ | ++ | + |
| DLB | + | + | ++ | +++ | + | + |
| FTD (tau) | - | + (4R) | ++ | ++ | - | - |
| FTD (TDP) | - | - | ++ | ++ | - | - |
| Vascular dementia | - | - | + | + | ++ | + |

Commercial Availability

| Panel | Provider | Markers | Status |
|-------|----------|---------|--------|
| A-T-N+ Panel | Quanterix | p-Tau181, NfL, GFAP | RUO |
| Neurology 4-Plex | MSD | Aβ, p-Tau, NfL, GFAP | RUO |
| Simoa Synaptic Panel | Quanterix | Ng, SNAP-25, NPTX1 | RUO |
| Microglial Panel | Alango | sTREM2, YKL-40, CHIT1 | RUO |

Research Directions

• Multiplexed single-molecule arrays enabling 10+ markers from single blood draw
• Machine learning integration combining biomarkers with clinical data for risk scores
• Point-of-care devices for rapid A/T(N)+ screening in primary care
• Longitudinal tracking using home-based sampling for progression monitoring

Cross-Links

• [AT(N) Biomarker Classification](/biomarkers/atn-biomarker-classification-ad)
• [Plasma p-Tau217](/biomarkers/p-tau-217)
• [CSF Neurofilament Light Chain](/biomarkers/neurofilament-light-chain)
• [GFAP in Alzheimer's](/biomarkers/gfap-alzheimers)
• [Synaptic Biomarkers](/biomarkers/synaptic-biomarkers-alzheimers)
• [sTREM2 Biomarker](/biomarkers/strem2-soluble-trem2)
• [Combination Biomarker Panels AD](/biomarkers/combination-biomarker-panels-ad)

References

See Also

• [Neural Circuits in Dementia with Lewy Bodies](/wiki/circuits-dementia-with-lewy-bodies-circuits) — causes
• [Proteome Atlas for Neurodegenerative Diseases](/wiki/datasets-proteome-atlas-neurodegenerative-diseases) — regulates
• [First-in-Human 4R Tau Ligand Study in PSP (NCT07348276)](/wiki/clinical-trials-first-human-4r-tau-ligand-psp-nct07348276) — associated_with
• [Neurodegeneration](/wiki/diseases-neurodegeneration) — causes
• [First-in-Human 4R Tau Ligand Study in PSP (NCT07348276)](/wiki/clinical-trials-first-human-4r-tau-ligand-psp-nct07348276) — causes

Pathway Diagram

The following diagram shows the key molecular relationships involving A/T/N+ Comprehensive Biomarker Panel for Alzheimer's Disease Staging discovered through SciDEX knowledge graph analysis: