Biomarker Types Overview is a topic within the NeuroWiki knowledge base covering aspects of neurodegenerative disease research and mechanisms.
Biomarkers are measurable indicators of biological processes, disease states, or therapeutic responses. In neurodegenerative diseases, biomarkers provide objective measures of pathology, enable early detection, track disease progression, and evaluate treatment effects. This overview covers the major biomarker categories used in Alzheimer's disease, Parkinson's disease, ALS, and other neurodegenerative conditions.
Fluid biomarkers are measured in cerebrospinal fluid (CSF), blood (plasma/serum), or other bodily fluids.
CSF directly reflects brain biochemistry through the blood-brain barrier 1.
Alzheimer's Disease Biomarkers:
- Amyloid-beta 42: Decreased in AD due to plaque deposition; 50-70% reduction compared to controls 2
- Amyloid-beta 40: Reference peptide; Aβ42/40 ratio improves accuracy
- Total tau (t-tau): Elevated in AD; reflects neuronal damage
- Phosphorylated tau (p-tau): AD-specific; correlates with neurofibrillary tangles 3
Parkinson's Disease Biomarkers:
- Neurofilament light chain (NfL): Marker of axonal degeneration; elevated in PD and atypical parkinsonism 4
- Alpha-synuclein: Total and phosphorylated forms; seeding assays detect pathology
ALS Biomarkers:
- Neurofilament light chain (NfL): Prognostic marker; higher levels = faster progression
- Phosphorylated neurofilament heavy chain (pNfH): Disease severity marker
Blood tests are less invasive and suitable for screening.
Key Blood Biomarkers:
- p-tau181: Highly accurate for AD; correlates with amyloid and tau PET 5
- p-tau217: May be even more specific than p-tau181; detects early AD 6
- NfL: Cross-disease marker of neurodegeneration; validated in many studies 7
- GFAP: Astrocyte marker; elevated in AD
Neuroimaging provides structural and molecular information.
MRI Biomarkers:
- Hippocampal atrophy: Key AD marker; measured by hippocampal volume 8
- Ventricular enlargement: Marker of brain volume loss
- White matter hyperintensities: Vascular contributions
- Regional atrophy patterns: Differentiates AD, FTD, DLB
Amyloid PET:
- Tracers: Florbetapir, flutemetamol, florbetaben
- Detects amyloid plaques in vivo
- Sensitivity >95%, specificity >90% 9
Tau PET:
- Primary tracer: Flortaucipir (Avid)
- Visualizes neurofibrillary tangles
- Correlates with clinical severity 10
Dopamine Imaging:
- DaT-SPECT: Confirms dopaminergic deficit in PD
- PET tracers: F-DOPA, CFT
Genetic markers identify risk and confirm diagnosis.
Risk Factors:
- APOE ε4: Strongest AD risk allele; 3-4x increased risk 11
- LRRK2 G2019S: Most common PD mutation
- GBA: Carriers have increased PD risk and earlier onset
- C9orf72: Most common ALS/FTD mutation
Monogenic Forms:
- APP, PSEN1, PSEN2: Autosomal dominant AD
- SNCA, LRRK2, GBA, PARK2: Monogenic PD
- SOD1, FUS, C9orf72: Familial ALS
Emerging technologies enable continuous monitoring.
Motion Sensors:
- Accelerometers detect tremor, bradykinesia
- Gait analysis identifies subtle changes
- Activity monitoring tracks overall function 12
Voice and Speech Analysis:
- Reduced vocal complexity in PD
- Speech rate changes in AD
- Machine learning improves detection
Sleep Monitoring:
- REM sleep behavior disorder (RBD) - prodromal PD/PD
- Sleep fragmentation common in neurodegeneration
Standardized clinical measures serve as biomarkers.
Cognitive Assessments:
- MMSE, MoCA: Global cognition
- CDR: Dementia staging
- Executive function tests: Frontotemporal involvement
Motor Assessments:
- UPDRS: PD severity
- ALSFRS-R: ALS functional rating
- Timed up and go: Mobility
| Biomarker |
Type |
Clinical Use |
| Amyloid PET |
Imaging |
Diagnosis |
| CSF Aβ42 |
Fluid |
Diagnosis |
| CSF p-tau |
Fluid |
Diagnosis, monitoring |
| Blood p-tau |
Fluid |
Screening |
| MRI atrophy |
Imaging |
Staging |
| Biomarker |
Type |
Clinical Use |
| DaT-SPECT |
Imaging |
Diagnosis |
| NfL |
Fluid |
Prognosis |
| Alpha-syn RT-QuIC |
Fluid |
Diagnosis |
| Genetic testing |
Genetic |
Risk, diagnosis |
| Biomarker |
Type |
Clinical Use |
| EMG |
Clinical |
Diagnosis |
| NfL |
Fluid |
Prognosis |
| pNfH |
Fluid |
Monitoring |
| Genetic testing |
Genetic |
Diagnosis, family planning |
The AT(N) system standardizes biomarker reporting 13:
- A: Amyloid biomarkers (Aβ PET, CSF Aβ42)
- T: Tau biomarkers (tau PET, CSF p-tau)
- (N): Neurodegeneration (MRI atrophy, FDG-PET, CSF t-tau)
Biomarkers can detect disease stages:
- Preclinical: Biomarker abnormal, no symptoms
- MCI: Mild cognitive impairment, biomarker positive
- Dementia: Clinical syndrome, biomarker confirmed
- Proteomics: Unbiased discovery of new markers
- Exosomes: Brain-derived vesicles for specific signals
- Multimodal AI: Combine biomarkers for precision
- Blood biomarkers for population screening
- Point-of-care testing
- Digital biomarker integration