AT(N) Biomarker Classification-Guided Alzheimer's Disease Therapy represents a paradigm shift in AD treatment, using the amyloid/tau/neurodegeneration (AT(N)) biomarker framework to precisely categorize patients and match them to targeted therapies based on their specific pathological profile[@niaaa2023][@biomarkerguided2024].
The NIA-AA Research Framework classifies AD biomarkers into three core pathological domains[@jack2018][@hansson2019]:
| Domain | Biomarkers | What It Measures |
|---|---|---|
| A (Amyloid) | Aβ42/40 in CSF/Plasma, Amyloid PET | Amyloid plaque pathology |
| T (Tau) | p-Tau181/217/231 in CSF/Plasma, Tau PET | Tau neurofibrillary tangles |
| (N) (Neurodegeneration) | t-Tau, NfL, Neurogranin, FDG-PET, MRI | Neuronal injury, synaptic loss, atrophy |
AT(N) profiling enables biologically-based diagnosis that transcends clinical symptoms:
Clinical Profile: Dementia due to AD, moderate-to-severe cognitive impairment
Recommended Therapy:
Evidence: CLARITY-AD and TRAILBLAZER-ALZ 2 trials showed greatest benefit in patients with confirmed A+T+ pathology[@cummings2023][@van2023]. Biomarker-confirmed enrollment improved effect sizes by 20-30%.
Clinical Profile: MCI due to AD or early dementia, preserved function
Recommended Therapy:
Rationale: Patients without neurodegeneration may have the best response to amyloid removal before irreversible neuronal loss[@mintun2021]. This group showed the largest treatment effects in anti-amyloid trials.
Clinical Profile: Cognitive impairment without AD-specific pathology
Recommended Therapy:
Important: Anti-amyloid therapy is NOT indicated for SNAP[@salloway2022].
Clinical Profile: PSP, CBD, FTLD-tau clinical phenotypes
Recommended Therapy:
Note: Anti-amyloid therapy is NOT indicated in primary tauopathies.
| Clinical Scenario | Required Biomarkers | Optional |
|---|---|---|
| Suspected early AD | Blood Aβ42/40, p-Tau217 | CSF confirm |
| Typical AD dementia | A+T+(N) profile | Full panel |
| Atypical presentation | Full AT(N) + α-syn | Genetic |
| Treatment monitoring | Serial p-Tau, NfL | Amyloid PET |
Biomarker-Guided Treatment Monitoring:
| Timepoint | Biomarkers to Monitor | Expected Changes |
|---|---|---|
| Baseline | Full AT(N) profile | Establishes eligibility |
| 3-6 months | Plasma p-Tau, Aβ42/40 | Target engagement |
| 12 months | Repeat AT(N) | Disease modification assessment |
| Ongoing | NfL, p-Tau trajectory | Progression tracking |
Anti-amyloid trials have demonstrated that biomarker-confirmed enrollment improves signal detection[@schott2023]:
| Biomarker Profile | Expected Anti-Amyloid Response | Evidence Level |
|---|---|---|
| A+T+(N)+ | Moderate benefit | High |
| A+T+(N)- | Maximum benefit | High |
| A+T-(N)+ | No benefit | High |
| A-T+ any N | No benefit | Moderate |
ARIA (Amyloid-Related Imaging Abnormalities) risk varies by biomarker profile[@ryman2024]:
| Risk Factor | ARIA-E Risk | ARIA-H Risk |
|---|---|---|
| APOE ε4 carrier | 2-3x higher | 2x higher |
| High amyloid burden | Slightly increased | Increased |
| Pre-existing microhemorrhages | - | Higher |
| (N)+ with atrophy | Higher | Higher |
Advances in plasma biomarkers are enabling practical AT(N) profiling:
| Plasma Biomarker | Measures | Performance |
|---|---|---|
| Aβ42/40 ratio | A domain | AUC 0.85-0.90 |
| p-Tau217 | T domain | AUC 0.90-0.95 |
| p-Tau181 | T domain | AUC 0.85-0.92 |
| NfL | (N) domain | AUC 0.80-0.88 |
| GFAP | (N) domain | AUC 0.80-85 |
Practical advantage: Blood-based panels can accomplish AT(N) classification at $200-500 vs. $3000-7000 for PET imaging[@palmqvist2020].
AT(N) profiles guide combination approaches: