# Domain Expert Evaluation: BBB Permeability as Neurodegeneration Biomarker
## 1. Hypotheses with Highest Translational Potential
### Tier 1: Plasma GFAP/NFL as Accessible BBB Permeability Markers
**Current Clinical Evidence:**
GFAP elevation in plasma has demonstrated consistent associations with early AD pathology in the A4 trial (PMID: 36918366) and DIAN cohort. GFAP appears to rise *before* plasma p-tau changes in autosomal dominant AD, suggesting it captures a pathologically upstream process. NFL provides complementary neuroaxonal injury readouts with established analyte stability and CLIA-validated assays commercially available.
The translational infrastructure is essentially complete: blood collection requires no lumbar puncture, samples can be shipped frozen, and CROs already have operational pipelines for these biomarkers in current Phase 2/3 trials.
**Safety Considerations:**
Minimal. Blood collection carries negligible risk. However, interpretational caution is needed—GFAP elevations can reflect systemic inflammatory conditions, traumatic brain injury, or vascular comorbidities. Clear exclusion criteria and appropriate control populations are essential.
**Patient Population Fit:**
Perfectly aligned. The preclinical AD staging framework (AT(N)) already identifies