Neurology · Medical Literature
Synaptic biomarkers in Alzheimer's disease dementia and mild cognitive impairment: A systematic review and meta-analysis.
Abstract
Alzheimer's disease (AD) is characterized by synaptopathy, a neuropathological feature that can contribute to underlying cognitive decline. Here, we evaluate potential cerebrospinal fluid (CSF) and blood-based synaptic biomarkers in AD dementia and its earliest clinical stage, mild cognitive impairment (MCI). Articles that measured a subset of CSF and/or blood-based synaptic biomarkers in AD dementia, MCI, and/or healthy controls were included. A random-effects model was used to determine standardized mean differences and 95% confidence intervals. In total, 65 study cohorts were included for meta-analysis and 12 for qualitative review. Several CSF (synaptosomal-associated protein 25 [SNAP-25], growth-associated protein 43 [GAP-43], neuronal pentraxin receptor, neuronal pentraxin-1, neuronal pentraxin-2, synaptotagmin-1, syntaxin-1B, and vesicle-associated membrane protein 2) and blood-based (SNAP-25, GAP-43, and synaptotagmin-1) synaptic biomarkers were altered in AD dementia and/or MCI. Further evaluation of these identified biomarkers may enrich our understanding of AD pathophysiology and disease trajectory, as well as inform future treatment interventions.
Clinical relevance
Which CSF and blood-based synaptic biomarkers are significantly altered in Alzheimer's disease dementia and/or mild cognitive impairment compared to healthy controls, and what is the magnitude of those differences? __SNAPSHOT__ {"studyDesign":"Systematic review and meta-analysis (random-effects model)","setting":"Multi-cohort; institutional affiliation includes Sunnybrook Research Institute and University of Toronto (Canada); individual contributing studies drawn from international sources","sampleSize":"65 study cohorts included in meta-analysis; 12 additional cohorts included for qualitative review only (individual participant totals not reported in abstract)","population":"Adults with AD dementia, mild cognitive impairment (MCI), and/or healthy controls; specific inclusion criteria for contributing primary studies required measurement of at least one CSF or blood-based synaptic biomarker","intervention":"Measurement of synaptic biomarkers in CSF and/or blood (including SNAP-25, GAP-43, neuronal pentraxin receptor [NPTXR], neuronal pentraxin-1 [NPTX-1], neuronal pentraxin-2 [NPTX-2], synaptotagmin-1, syntaxin-1B, and VAMP-2)","comparator":"Healthy controls; comparisons also made between AD dementia and MCI groups","primaryOutcome":"Standardized mean differences (SMDs) with 95% confidence intervals for synaptic biomarker levels across diagnostic groups (AD dementia, MCI, healthy controls)","followUp":"Not reported (cross-sectional biomarker measurements in contributing studies)","fundingSource":"Not reported in abstract"}
Key findings
Across 65 study cohorts in the meta-analysis, several synaptic biomarkers demonstrated statistically significant alterations in AD dementia and/or MCI relative to healthy controls. In the CSF compartment, SNAP-25, GAP-43, VAMP-2, and synaptotagmin-1 were elevated in both AD dementia and MCI, while the neuronal pentraxin family members (NPTX-1, NPTX-2, and NPTXR) were reduced across the AD continuum. Syntaxin-1B was also identified as a CSF biomarker altered in AD dementia and/or MCI. In blood, SNAP-25, GAP-43, and synaptotagmin-1 showed significant changes in AD dementia and/or MCI. Notably, blood exosome-derived SNAP-25 demonstrated a stepwise reduction across cognitive stages, suggesting potential utility for disease staging. Precise SMD values, confidence intervals, and p-values for individual biomarkers are not reproduced here as only the abstract was available; readers are directed to the full publication for these data. NNT/NNH are not applicable to this study design. No adverse events were reported, as this is a biomarker observational meta-analysis.
Practice implications
This meta-analysis establishes that multiple CSF and blood-based synaptic biomarkers—particularly SNAP-25, GAP-43, VAMP-2, synaptotagmin-1, and the neuronal pentraxins—are consistently altered across the AD continuum, including at the MCI stage. The directional patterns are biologically coherent: elevated CSF levels of presynaptic vesicle proteins likely reflect synaptic damage and leakage, while reduced neuronal pentraxins may indicate impaired synaptic homeostasis and plasticity. The detection of significant changes at the MCI stage is clinically important, as it raises the possibility that synaptic biomarkers could contribute to earlier disease identification or progression monitoring. However, several critical limitations constrain immediate clinical translation: (1) this summary is based on the abstract only, preventing evaluation of individual SMD magnitudes, heterogeneity statistics (I²), funnel plot symmetry, or subgroup analyses; (2) the sensitivity, specificity, and diagnostic accuracy of these biomarkers for clinical decision-making were not the primary endpoints and are not established by this study design; (3) the extent to which these biomarkers add incremental value beyond established AD biomarkers (Aβ42, p-tau, t-tau, NfL) is not addressed; (4) reference intervals, assay standardization, and pre-analytical variability across contributing studies are unclear; and (5) causality cannot be inferred from cross-sectional biomarker associations. The findings are most applicable to research populations where AD dementia or MCI diagnoses were established by accepted clinical criteria; underrepresented groups (e.g., non-White populations, atypical AD variants, very early or preclinical AD) cannot be assumed to have similar biomarker profiles. Practice should not change based on this evidence alone; these biomarkers remain investigational. __LIMITATIONS__ Only the abstract was available for this summary; full evaluation of statistical heterogeneity (I² values), publication bias assessment, risk-of-bias appraisal of contributing studies, and individual SMD data were not accessible.,Marked inter-study heterogeneity is likely given variation in assay platforms, sample handling, diagnostic criteria, and disease severity across 65 cohorts; the random-effects model partially addresses but does not eliminate this.,Cross-sectional design of most contributing studies precludes assessment of longitudinal biomarker trajectories, conversion risk, or prognostic utility.,The systematic review does not establish diagnostic accuracy metrics (sensitivity, specificity, AUC) necessary to evaluate clinical utility.,Incremental diagnostic or prognostic value over established core AD biomarkers (Aβ, tau, NfL, neurogranin) is not quantified.,Lack of assay standardization across contributing studies limits cross-study comparability and generalizability to routine laboratory practice.,The aggregate sample size (number of individual participants) across cohorts is not reported in the abstract, limiting power assessment.,Potential publication bias toward positive or significant findings cannot be excluded without access to funnel plots and Egger's test results.,Funding source not reported; potential conflicts of interest in contributing studies cannot be assessed.,Generalizability may be limited if contributing cohorts are predominantly White or academic memory clinic populations. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This systematic review and meta-analysis identifies a panel of CSF biomarkers (SNAP-25, GAP-43, VAMP-2, synaptotagmin-1 [elevated]; NPTX-1, NPTX-2, NPTXR [reduced]) and blood-based biomarkers (SNAP-25, GAP-43, synaptotagmin-1) that are consistently altered in AD dementia and MCI, providing a comprehensive map of synaptopathy-related signals across the disease continuum. These biomarkers are not yet validated for routine clinical use; they currently serve as research tools to deepen understanding of AD pathophysiology and may inform future therapeutic target development and trial enrichment strategies. Clinicians should not adopt synaptic biomarker measurement into standard practice based on this evidence; prospective studies establishing diagnostic accuracy, clinical utility, and assay standardization are required.