<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">N-of-1 and Personalized Clinical Trial Design for CBS/PSP</th>
</tr>
<tr>
<td class="label">Domain</td>
<td>Instrument</td>
</tr>
<tr>
<td class="label">Motor function</td>
<td>PSPRS (PSP)[@golbe2014], CBSI (CBS)[@matsuo2009]</td>
</tr>
<tr>
<td class="label">Gait/balance</td>
<td>Tinetti POMA[@tinetti1986], 10m walk</td>
</tr>
<tr>
<td class="label">Cognition</td>
<td>FAB[@dubois2000], MoCA[@nasreddine2005]</td>
</tr>
<tr>
<td class="label">Biomarker</td>
<td>Plasma p-tau217[@janelidze2020], NfL[@bublok2022]</td>
</tr>
<tr>
<td class="label">Caregiver burden</td>
<td>Zarit Burden Interview[@zarit1980]</td>
</tr>
<tr>
<td class="label">Platform</td>
<td>Throughput</td>
</tr>
<tr>
<td class="label">High-content imaging</td>
<td>~1000 wells/ plate</td>
</tr>
<tr>
<td class="label">Flow cytometry</td>
<td>~10,000 cells/sample</td>
</tr>
<tr>
<td class="label">Seahorse bioenergetics</td>
<td>96-well</td>
</tr>
<tr>
<td class="label">Multi-electrode array (MEA)</td>
<td>768 channels</td>
</tr>
<tr>
<td class="label">Biomarker</td>
<td>Source</td>
</tr>
<tr>
<td class="label">p-tau217</td>
<td>Plasma/CSF</td>
</tr>
<tr>
<td class="label">p-tau181</td>
<td>Plasma/CSF</td>
</tr>
<tr>
<td class="label">NfL</td>
<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">N-of-1 and Personalized Clinical Trial Design for CBS/PSP</th>
</tr>
<tr>
<td class="label">Domain</td>
<td>Instrument</td>
</tr>
<tr>
<td class="label">Motor function</td>
<td>PSPRS (PSP)[@golbe2014], CBSI (CBS)[@matsuo2009]</td>
</tr>
<tr>
<td class="label">Gait/balance</td>
<td>Tinetti POMA[@tinetti1986], 10m walk</td>
</tr>
<tr>
<td class="label">Cognition</td>
<td>FAB[@dubois2000], MoCA[@nasreddine2005]</td>
</tr>
<tr>
<td class="label">Biomarker</td>
<td>Plasma p-tau217[@janelidze2020], NfL[@bublok2022]</td>
</tr>
<tr>
<td class="label">Caregiver burden</td>
<td>Zarit Burden Interview[@zarit1980]</td>
</tr>
<tr>
<td class="label">Platform</td>
<td>Throughput</td>
</tr>
<tr>
<td class="label">High-content imaging</td>
<td>~1000 wells/ plate</td>
</tr>
<tr>
<td class="label">Flow cytometry</td>
<td>~10,000 cells/sample</td>
</tr>
<tr>
<td class="label">Seahorse bioenergetics</td>
<td>96-well</td>
</tr>
<tr>
<td class="label">Multi-electrode array (MEA)</td>
<td>768 channels</td>
</tr>
<tr>
<td class="label">Biomarker</td>
<td>Source</td>
</tr>
<tr>
<td class="label">p-tau217</td>
<td>Plasma/CSF</td>
</tr>
<tr>
<td class="label">p-tau181</td>
<td>Plasma/CSF</td>
</tr>
<tr>
<td class="label">NfL</td>
<td>Plasma/CSF</td>
</tr>
<tr>
<td class="label">YKL-40</td>
<td>CSF</td>
</tr>
<tr>
<td class="label">Alpha-synuclein</td>
<td>CSF</td>
</tr>
<tr>
<td class="label">Pathway</td>
<td>When to Use</td>
</tr>
<tr>
<td class="label">Individual expanded access (EA1)</td>
<td>Single patient, not in trial</td>
</tr>
<tr>
<td class="label">Intermediate population (EA2)</td>
<td>Small group, serious condition</td>
</tr>
<tr>
<td class="label">Treatment IND/BAA (EA3)</td>
<td>Large group, life-threatening</td>
</tr>
<tr>
<td class="label">Right-to-Try Act (2018)</td>
<td>Terminal illness</td>
</tr>
<tr>
<td class="label">Jurisdiction</td>
<td>Pathway</td>
</tr>
<tr>
<td class="label">FDA (US)</td>
<td>Individual IND, Right-to-Try</td>
</tr>
<tr>
<td class="label">EMA (EU)</td>
<td>Named Patient Use, Compassionate Use</td>
</tr>
<tr>
<td class="label">Japan (PMDA)</td>
<td>Special Approval for Health Needs</td>
</tr>
<tr>
<td class="label">UK (MHRA)</td>
<td>Early Access to Medicines Scheme (EAMS)</td>
</tr>
<tr>
<td class="label">Phase</td>
<td>Duration</td>
</tr>
<tr>
<td class="label">Patient identification and enrichment</td>
<td>2-4 weeks</td>
</tr>
<tr>
<td class="label">IRB protocol preparation and review</td>
<td>2-4 weeks</td>
</tr>
<tr>
<td class="label">Drug procurement and formulation</td>
<td>2-8 weeks</td>
</tr>
<tr>
<td class="label">Baseline period and randomization</td>
<td>1-2 weeks</td>
</tr>
<tr>
<td class="label">Crossover periods</td>
<td>12-20 weeks</td>
</tr>
<tr>
<td class="label">Final assessment and analysis</td>
<td>2-4 weeks</td>
</tr>
<tr>
<td class="label">Total</td>
<td>4-8 months</td>
</tr>
<tr>
<td class="label">Phase</td>
<td>Duration</td>
</tr>
<tr>
<td class="label">Patient cell collection</td>
<td>1-2 weeks</td>
</tr>
<tr>
<td class="label">Reprogramming</td>
<td>4-6 weeks</td>
</tr>
<tr>
<td class="label">Characterization</td>
<td>2-4 weeks</td>
</tr>
<tr>
<td class="label">Neuronal differentiation</td>
<td>8-12 weeks</td>
</tr>
<tr>
<td class="label">Phenotype validation</td>
<td>2-4 weeks</td>
</tr>
<tr>
<td class="label">Drug screening</td>
<td>4-8 weeks</td>
</tr>
<tr>
<td class="label">Analysis and report</td>
<td>2-4 weeks</td>
</tr>
<tr>
<td class="label">Total</td>
<td>6-9 months</td>
</tr>
<tr>
<td class="label">Component</td>
<td>Cost Range</td>
</tr>
<tr>
<td class="label">Single-patient IRB protocol and review</td>
<td>$5,000-20,000</td>
</tr>
<tr>
<td class="label">Drug procurement (repurposed agent)</td>
<td>$0-10,000</td>
</tr>
<tr>
<td class="label">Drug procurement (investigational)</td>
<td>$10,000-100,000+</td>
</tr>
<tr>
<td class="label">Clinical outcome assessments</td>
<td>$5,000-15,000</td>
</tr>
<tr>
<td class="label">iPSC reprogramming and screening</td>
<td>$50,000-200,000</td>
</tr>
<tr>
<td class="label">Biomarker testing (plasma/CSF)</td>
<td>$2,000-10,000</td>
</tr>
<tr>
<td class="label">Total N-of-1 trial</td>
<td>$20,000-150,000</td>
</tr>
<tr>
<td class="label">Total with iPSC screen</td>
<td>$70,000-350,000</td>
</tr>
</table>
Corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP) are rare, rapidly progressive 4R-tauopathies with no disease-modifying treatments approved to date. The rarity of these conditions — PSP affects approximately 5-7 per 100,000 people[@espinosa2023], and CBS is even rarer — makes traditional large-scale randomized controlled trials (RCTs) infeasible. This creates a fundamental tension: the patients who need treatments most are too few for conventional trial infrastructure.
N-of-1 and personalized trial designs offer a solution. These approaches individualize treatment evaluation, enabling even single patients to generate meaningful evidence about therapeutic response. Originally pioneered in oncology and rare genetic diseases, the same frameworks apply directly to CBS/PSP, where patient-specific factors — genetic background, tau isoform expression, comorbidities, and baseline disability — dramatically affect treatment response.
This page covers the complete methodology for personalized clinical trials in CBS/PSP, from N-of-1 design principles through iPSC-derived drug screening, compassionate use pathways, regulatory frameworks, and practical case studies from oncology.
An N-of-1 trial is a randomized, double-blind, crossover experiment conducted in a single patient[@guyatt1986]. It compares an investigational treatment to placebo (or an active comparator) in repeated cycles, allowing each patient to serve as their own control. N-of-1 trials provide the highest level of individual evidence — better than case reports, better than observational data — while maintaining scientific rigor.
For CBS/PSP patients, N-of-1 trials address several critical gaps:
A CBS/PSP N-of-1 trial typically follows this structure:
Primary endpoints must be sensitive to individual change over short periods. Recommended measures include:
N-of-1 trials use within-patient comparison, typically via:
For a single patient, p-values are interpreted with caution. Even with N-of-1, a treatment demonstrating consistent, meaningful benefit across 2-3 cycles provides strong evidence for individual use, especially when corroborated by biomarker changes.
N-of-1 trials are not appropriate for all scenarios:
Induced pluripotent stem cells (iPSCs) derived from a patient's own cells (typically fibroblasts or blood) can be differentiated into cortical neurons, dopaminergic neurons, or astrocytes[@takahashi2007]. These patient-specific neurons retain the individual's genetic background and can manifest disease-relevant phenotypes — including tau aggregation, mitochondrial dysfunction, and synaptic loss — in a dish.
For CBS/PSP, iPSC screens offer:
The field has made significant progress generating 4R-tauopathy models from iPSCs:
iPSC screening for CBS/PSP remains in the translational research phase:
Blood and CSF biomarkers enable real-time adaptation of trial enrollment and dose selection without invasive procedures:
Using biomarker thresholds to adapt trial enrollment mid-study:
Basket trial designs — pioneered in oncology for molecularly-defined cohorts — apply naturally to 4R-tauopathies:
The FDA provides three pathways for access to investigational treatments outside clinical trials:
For CBS/PSP patients, the most relevant pathway is individual expanded access (EA1), which allows a treating physician to request a single-patient IND for a patient who:
The treating physician submits Form FDA 3926 (individual new drug IND) to the FDA, which must respond within 30 days (typically within 1-2 weeks for serious conditions). Key elements:
Several investigational agents have been used via expanded access in tauopathy patients:
Single-patient (n-of-1) trials conducted outside a formal IND require IRB oversight to protect the patient and establish ethical legitimacy. Most US academic medical centers have established single-patient trial IRB pathways:
Expedited review (not full board): Single-patient protocols can often be reviewed by the IRB chair or designee under the "minimal risk, minor change" category, reducing review time from 30+ days to 3-7 days.
The single-patient IRB protocol should include:
A 65-year-old patient with CBS, MAPT P301L mutation, elevated plasma p-tau217, and progressive motor decline:
N-of-1 trials in CBS/PSP raise specific ethical considerations beyond standard clinical trial ethics:
Vulnerable Population Protection: CBS/PSP patients have progressive cognitive and motor decline, potentially impairing informed consent capacity over time. The ethical framework must:
CBS/PSP pathophysiology involves multiple convergent mechanisms — tau aggregation, neuroinflammation, mitochondrial dysfunction, proteostatic failure. Monotherapy targeting a single mechanism is unlikely to arrest disease. Combination therapy raises the stakes for trial design:
The accelerated approval pathway allows FDA approval based on a surrogate endpoint reasonably likely to predict clinical benefit, with post-marketing confirmation. For CBS/PSP:
When combining multiple investigational agents:
Oncology has pioneered personalized medicine approaches that directly inform CBS/PSP strategy.
Background: Vemurafenib (BRAF V600E inhibitor) was tested in melanoma patients with the BRAF mutation[@chapman2011]. Initial N-of-1 dose-escalation studies in selected patients established proof of concept. The subsequent BRIM-3 trial led to accelerated FDA approval in 2011, with confirmatory Phase 4 data.
Relevance to CBS/PSP: Similarly, MAPT mutation carriers represent a molecularly-defined subpopulation within the PSP/CBS spectrum. An agent targeting the mutant tau protein would first demonstrate efficacy in this subgroup before broader enrollment.
Background: Pembrolizumab (anti-PD-1) received accelerated approval for tumors with PD-L1 expression ≥50%[@topalian2016]. The KEYNOTE-001 trial used biomarker-driven enrichment — patients were stratified by PD-L1 expression, and the treatment effect was dramatically larger in high-expression patients. Subsequent trials confirmed this finding and expanded the indication.
Relevance to CBS/PSP: Plasma p-tau217 and CSF NfL serve as analogous biomarkers for tauopathy trials. Enriching for high biomarker expressing patients could double the signal-to-noise ratio in early trials.
Background: Larotrectinib received accelerated approval for tumors harboring NTRK gene fusions regardless of tissue of origin[@drilon2018]. This "tissue-agnostic" basket trial enrolled based on molecular alteration, not cancer type. The ORR was 75% across 17 tumor types.
Relevance to CBS/PSP: Similarly, a tau aggregation inhibitor might be effective across the CBS/PSP/FTD spectrum based on the shared 4R-tau pathology, regardless of the clinical syndrome label.
Background: Following the Right-to-Try Act, oncology patients with exhausted options have accessed investigational drugs directly through physicians, without FDA involvement. Reports from the Goldwater Institute documented hundreds of patients accessing drugs via this pathway.
Relevance to CBS/PSP: CBS patients with median survival of 6-7 years have exhausted standard treatment options. Right-to-try provides a direct route to investigational agents, though without FDA oversight the safety data collection is less rigorous.
Related Hypotheses:
From the [SciDEX Exchange](/exchange) — scored by multi-agent debate
Related Analyses: