MicroRNAs (miRNAs) are small non-coding RNA molecules (18-25 nucleotides) that regulate gene expression post-transcriptionally. In neurodegenerative diseases, specific miRNA signatures in cerebrospinal fluid (CSF), blood, and tissue have emerged as promising biomarkers for diagnosis, disease progression, and therapeutic response monitoring. These molecules offer advantages as biomarkers due to their stability in biological fluids, disease-specific expression patterns, and potential for non-invasive detection. [@jung2022]
MicroRNAs play critical roles in neuronal development, synaptic plasticity, and immune regulation. Dysregulation of specific miRNAs has been implicated in the pathogenesis of Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD). The measurement of circulating miRNAs in CSF and blood provides a window into CNS pathology that is otherwise difficult to access. [@chen2023]
The field of miRNA biomarkers has advanced significantly with the development of highly sensitive detection platforms and large-scale validation studies across diverse populations. Recent research has focused on identifying miRNA signatures that can distinguish between neurodegenerative diseases, predict disease progression, and monitor therapeutic responses.
MicroRNAs (miRNAs) are small non-coding RNA molecules (18-25 nucleotides) that regulate gene expression post-transcriptionally. In neurodegenerative diseases, specific miRNA signatures in cerebrospinal fluid (CSF), blood, and tissue have emerged as promising biomarkers for diagnosis, disease progression, and therapeutic response monitoring. These molecules offer advantages as biomarkers due to their stability in biological fluids, disease-specific expression patterns, and potential for non-invasive detection. [@jung2022]
MicroRNAs play critical roles in neuronal development, synaptic plasticity, and immune regulation. Dysregulation of specific miRNAs has been implicated in the pathogenesis of Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD). The measurement of circulating miRNAs in CSF and blood provides a window into CNS pathology that is otherwise difficult to access. [@chen2023]
The field of miRNA biomarkers has advanced significantly with the development of highly sensitive detection platforms and large-scale validation studies across diverse populations. Recent research has focused on identifying miRNA signatures that can distinguish between neurodegenerative diseases, predict disease progression, and monitor therapeutic responses.
| miRNA | Expression | Sample Type | Diagnostic Utility | Sensitivity/Specificity |
|-------|------------|-------------|-------------------|------------------------|
| miR-191-5p | Downregulated | Blood | Cognitive decline, early AD | AUC 0.85-0.91 [@yang2024] |
| miR-9 | Downregulated | CSF, blood | Early AD detection | AUC 0.78-0.82 [@tanaka2022] |
| miR-29a/b | Downregulated | CSF | Aβ pathology correlation | AUC 0.75-0.81 |
| miR-125b | Upregulated | CSF, blood | Tau pathology, disease severity | AUC 0.72-0.79 |
| miR-146a | Upregulated | CSF, blood | Neuroinflammation, progression | AUC 0.68-0.76 |
| miR-155 | Upregulated | CSF, blood | Neuroinflammation, microglial activation | AUC 0.74-0.83 [@wei2023] |
The most extensively validated AD-specific miRNA is miR-191-5p, which shows consistent downregulation in AD patients. A 2024 study in a Chinese cohort demonstrated AUC values of 0.85-0.91 for distinguishing AD from controls, with sensitivity of 82% and specificity of 87% [@yang2024]. The combination of miR-191-5p with other markers improves diagnostic accuracy.
Multi-marker panels have shown superior performance. A 2024 Nature Aging study identified a 5-miRNA panel (miR-191-5p, miR-9, miR-125b, miR-146a, miR-29a) that achieved AUC 0.93 for AD vs. controls and AUC 0.89 for AD vs. other dementias [@wang2024].
| miRNA | Expression | Sample Type | Diagnostic Utility | Sensitivity/Specificity |
|-------|------------|-------------|-------------------|------------------------|
| miR-7 | Downregulated | Blood, CSF | α-Synuclein regulation | AUC 0.76-0.82 |
| miR-124 | Downregulated | Blood | Neuronal survival, autophagy | AUC 0.71-0.78 |
| miR-153 | Downregulated | Blood | α-Synuclein expression | AUC 0.73-0.79 |
| miR-29c | Downregulated | Blood | Disease progression | AUC 0.68-0.75 |
| miR-30 family | Downregulated | Blood | Mitochondrial function | AUC 0.70-0.77 |
| miR-133b | Downregulated | Blood, CSF | Dopaminergic neuron function | AUC 0.72-0.80 |
A 2023 Korean study validated serum miRNA signatures in 245 PD patients and 180 controls, identifying miR-124 and miR-7 as the most discriminative markers with combined AUC of 0.84 [@park2023]. Exosomal miR-7 and miR-153 from olfactory mucosa have shown promise for early PD detection, with sensitivity of 78% and specificity of 82% [@liu2023].
| miRNA | Expression | Sample Type | Diagnostic Utility | Sensitivity/Specificity |
|-------|------------|-------------|-------------------|------------------------|
| miR-9 | Downregulated | CSF | Motor neuron dysfunction | AUC 0.74-0.81 |
| miR-124 | Downregulated | Blood | Neuroinflammation | AUC 0.69-0.77 |
| miR-131 | Upregulated | CSF | Disease progression | AUC 0.71-0.79 |
| miR-143 | Upregulated | CSF | TDP-43 pathology | AUC 0.67-0.75 |
| miR-338-3p | Downregulated | Blood | Motor neuron survival | AUC 0.73-0.82 |
A Korean multicenter study of 156 ALS patients demonstrated that plasma miR-124 had an AUC of 0.77 for ALS vs. controls and could distinguish ALS from PD with AUC 0.72 [@kim2023]. The combination of miR-124 with miR-338-3p improved discrimination.
| Sample Type | Advantages | Disadvantages | Typical Volume |
|-------------|------------|---------------|----------------|
| CSF | Direct CNS access, highest specificity | Invasive (lumbar puncture) | 1-2 mL |
| Blood plasma | Non-invasive, stable | Lower CNS specificity | 1-5 mL |
| Blood serum | Non-invasive | Variable exosome recovery | 1-5 mL |
| PBMCs | Immune cell-specific | Requires processing | 5-10 mL |
| Exosomes | Enriched for CNS-derived | Specialized isolation | 0.5-1 mL |
| Olfactory mucosa | Non-invasive, direct CNS access | Variable collection | Swab |
A 2024 study in the Chinese cohort (n=312 AD, n=280 MCI, n=290 controls) identified miR-191-5p as a robust biomarker with AUC 0.91 (sensitivity 85%, specificity 88%) for AD vs. controls [@yang2024]. The study established population-specific cutoffs:
A 2024 J-ADNI substudy analyzed CSF miRNA profiles in 186 Japanese patients [@zhao2024]:
Korean studies have validated:
| Region | Status | Notes |
|--------|--------|-------|
| FDA | LDT only | No approved miRNA diagnostic tests yet |
| CE-IVD | In development | Several EU companies in validation |
| PMDA | Research use | Japanese studies ongoing |
| NMPA | Research use | Chinese cohort validations |
| Method | Cost (USD) | Turnaround | Clinical Availability |
|--------|------------|------------|----------------------|
| qRT-PCR | $50-150/test | 1-2 days | Widely available |
| NGS panel | $200-400 | 5-7 days | Reference labs |
| Digital PCR | $75-200 | 2-3 days | Limited |
| Simoa | $100-250 | 3-5 days | Specialized labs |
Comparison with other biomarkers:
miRNAs can be integrated into the AT(N) biomarker framework:
| AT(N) Domain | miRNA Markers | Clinical Significance |
|--------------|---------------|----------------------|
| A (Amyloid) | miR-29a/b, miR-9 | Correlate with Aβ42, PET |
| T (Tau) | miR-125b, miR-132 | Correlate with p-tau, tau PET |
| N (Neurodegeneration) | miR-191-5p, miR-124 | Correlate with NfL, atrophy |
The combination of AT(N) markers with miRNA panels provides comprehensive biological characterization of AD pathology.
| Panel Composition | AUC (AD vs. Control) | AUC (AD vs. Other) |
|-------------------|---------------------|-------------------|
| miR-191 + miR-9 + miR-125b | 0.92 | 0.86 |
| miR-191 + miR-146a + miR-29a | 0.89 | 0.82 |
| miR-191 + miR-9 + miR-125b + miR-146a + miR-29a | 0.93 | 0.89 |
AI-based algorithms improve miRNA panel performance:
The following diagram shows the key molecular relationships involving MicroRNA (miRNA) Biomarkers in Neurodegenerative Disease discovered through SciDEX knowledge graph analysis: