Pre-Symptomatic Tau Detection in MAPT Mutation Carriers

Hypothesis

Primary Hypothesis: Tau pathology becomes detectable via blood-based biomarkers 5-10 years before clinical onset in individuals with pathogenic MAPT mutations, enabling pre-symptomatic intervention trials.

Secondary Hypotheses:

The sequence of biomarker abnormalities follows a predictable pattern: CSF p-tau217 → blood p-tau217 → CSF NfL → tau PET → clinical symptoms

Regional vulnerability in the brainstem (subsequently spreading to cortical regions) determines the timing of symptom onset

Genetic modifiers (other tauopathy risk alleles) modulate the age of onset in MAPT carriers

Open Question Source

This experiment addresses the critical unknown identified in the [CBS/PSP Cure Roadmap](/mechanisms/cbs-psp-cure-roadmap) Phase 5:

• "When does tau pathology begin relative to symptoms? (5 years? 10 years? 20 years?)"
• "Is there a 'point of no return' after which intervention is too late?"

Also addresses [AD Cure Roadmap](/mechanisms/ad-cure-roadmap) prevention questions:

• Validated pre-symptomatic biomarkers for early detection

Validation Protocol

Study Design

• Type: Multi-center prospective longitudinal biomarker study
• Cohort:
• MAPT mutation carriers (any pathogenic variant): n=150 (50 pre-symptomatic, 50 early-symptomatic, 50 moderate)
• Age-matched non-carrier family members: n=100 (controls)
• Sporadic PSP patients: n=50 (positive controls for biomarker validation)
• Follow-up: 5 years minimum, with optional extension to 10 years

Inclusion Criteria

...

Hypothesis

Primary Hypothesis: Tau pathology becomes detectable via blood-based biomarkers 5-10 years before clinical onset in individuals with pathogenic MAPT mutations, enabling pre-symptomatic intervention trials.

Secondary Hypotheses:

The sequence of biomarker abnormalities follows a predictable pattern: CSF p-tau217 → blood p-tau217 → CSF NfL → tau PET → clinical symptoms

Regional vulnerability in the brainstem (subsequently spreading to cortical regions) determines the timing of symptom onset

Genetic modifiers (other tauopathy risk alleles) modulate the age of onset in MAPT carriers

Open Question Source

This experiment addresses the critical unknown identified in the [CBS/PSP Cure Roadmap](/mechanisms/cbs-psp-cure-roadmap) Phase 5:

• "When does tau pathology begin relative to symptoms? (5 years? 10 years? 20 years?)"
• "Is there a 'point of no return' after which intervention is too late?"

Also addresses [AD Cure Roadmap](/mechanisms/ad-cure-roadmap) prevention questions:

• Validated pre-symptomatic biomarkers for early detection

Validation Protocol

Study Design

• Type: Multi-center prospective longitudinal biomarker study
• Cohort:
• MAPT mutation carriers (any pathogenic variant): n=150 (50 pre-symptomatic, 50 early-symptomatic, 50 moderate)
• Age-matched non-carrier family members: n=100 (controls)
• Sporadic PSP patients: n=50 (positive controls for biomarker validation)
• Follow-up: 5 years minimum, with optional extension to 10 years

Inclusion Criteria

Age 18-75 years

Either:

• Pathogenic MAPT mutation (confirmed by genetic testing) OR
• First-degree relative of MAPT mutation carrier

3. Able to undergo MRI and PET imaging

Willing to undergo genetic counseling

Exclusion Criteria

Current diagnosis of PSP, CBD, AD, or other neurodegenerative disease

Contraindications to MRI (pacemaker, metal implants)

Contraindications to PET (recent chemotherapy, pregnancy)

Active psychiatric condition requiring hospitalization

Biomarker Assessment Schedule

| Biomarker | Baseline | 6mo | 12mo | 18mo | 24mo | Year 3 | Year 4 | Year 5 |
|-----------|----------|-----|------|------|------|--------|--------|--------|
| Blood p-tau217 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Blood NfL | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Blood GFAP | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| CSF p-tau181/217 | ✓ | | ✓ | | ✓ | | ✓ | ✓ |
| CSF NfL | ✓ | | ✓ | | ✓ | | ✓ | ✓ |
| CSF total tau | ✓ | | ✓ | | ✓ | | ✓ | ✓ |
| Tau PET (flortaucipir) | ✓ | | | | ✓ | | | ✓ |
| MRI (T1, SWI, DTI) | ✓ | | ✓ | | ✓ | | ✓ | ✓ |
| Clinical assessment | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |

Clinical Assessments

Primary Outcome: Time to clinical conversion (PSP or CBS diagnosis)

Secondary Outcomes:

• PSP Rating Scale (PSPRS)
• MDS-UPDRS
• Cognitive batteries (MoCA, FAB, Trail Making A/B)
• CSF biomarker trajectories

Experimental Arm: Tau Kinetics Sub-Study

Aim 1: Validate Blood p-tau217 as Sensitive Biomarker

• Rationale: Blood p-tau217 has shown high accuracy for detecting tau pathology in AD; validate for 4R-tauopathies
• Methods:
• Compare sensitivity of blood p-tau217 vs CSF p-tau217 vs PET
• Establish cutoff values for pre-symptomatic detection
• Test correlation with tau PET regional uptake

Aim 2: Characterize Biomarker Temporal Sequence

• Rationale: Determine which biomarker becomes abnormal first
• Methods:
• Population-average biomarker trajectories
• Individual-level trajectory modeling (mixed-effects)
• Correlation with clinical conversion

Aim 3: Test Intervention Window Hypothesis

• Rationale: Determine whether pre-symptomatic intervention is feasible
• Methods:
• Modeling of biomarker slopes pre-conversion
• Simulation of trial power at different intervention timepoints
• Identification of optimal inclusion criteria for prevention trials

Expected Outcomes

Primary Outcomes

Biomarker detection window: p-tau217 detectable in blood at mean 7.2 years (95% CI: 4.2-10.1) before clinical conversion

Biomarker sequence: Blood p-tau217 → CSF NfL → tau PET → clinical symptoms (in that order)

Sensitivity/specificity: Blood p-tau217 for detecting pre-symptomatic tauopathy: 85% sensitivity, 90% specificity

Secondary Outcomes

Age of onset prediction model: R² > 0.7 for age of onset prediction using biomarker panel + genetic modifiers

Regional spread pattern: Tau PET identifies brainstem as initiation site in 80% of cases

Point of no return: Identify biomarker threshold beyond which intervention shows no benefit

Exploratory Outcomes

Genetic modifiers: Identify novel variants that modify age of onset

Environmental factors: Characterize lifestyle factors that modify biomarker trajectories

Sex differences: Characterize sex-based differences in biomarker patterns

Feasibility Assessment

Strengths

• Multi-center network (Cleveland Clinic, UCL, UCSF, Mayo Clinic) ensures adequate enrollment
• Existing MAPT family registries provide pre-identified participants
• Comprehensive biomarker panel enables detailed temporal mapping
• Integration with clinical trials infrastructure for future prevention studies

Challenges

• Rarity of MAPT mutations (estimated prevalence 1:100,000)
• Long follow-up required to capture conversions (may need 10+ years)
• Ethical considerations around predictive genetic testing
• Variable penetrance of MAPT mutations complicates age of onset prediction

Timeline

| Milestone | Expected Date |
|-----------|---------------|
| Protocol finalization | Month 1-3 |
| Site activation (4 sites) | Month 4-6 |
| First participant enrolled | Month 7 |
| 50% enrollment (100 total) | Month 18 |
| Full enrollment (250 total) | Month 30 |
| First clinical conversions expected | Month 24 (variable) |
| Primary analysis (5-year data) | Month 66 |

Cost Estimate

| Category | Cost (USD) |
|----------|------------|
| Personnel (3 FTE coordinators, 2 PI, 1 biostatistician) | $1,800,000 |
| Biomarker assays (blood, CSF) | $1,000,000 |
| Imaging (MRI, PET) | $800,000 |
| Clinical assessments | $300,000 |
| Genetic testing and counseling | $150,000 |
| Data management | $200,000 |
| Indirect costs (20%) | $850,000 |
| Total | $5,100,000 |

Cross-Disease Relevance

This experiment provides infrastructure and biomarkers relevant for:

• AD prevention trials (blood p-tau217 already validated for AD)
• PSP sporadic cases (biomarker validation)
• Other tauopathies (FTD, CBD)
• General neurodegeneration (NfL as general neuronal injury marker)

See Also

• [CBS/PSP Cure Roadmap](/mechanisms/cbs-psp-cure-roadmap)
• [AD Cure Roadmap](/mechanisms/ad-cure-roadmap)
• [Blood Biomarker for AD Detection](/experiments/blood-biomarker-ad-detection)
• [PSP/CBS Biomarker Validation](/experiments/psp-cbs-biomarker-validation)
• [Experiment Priority Index](/experiments/experiment-priority-index)

Pathway Diagram