| SNCA — Alpha-Synuclein | |
|---|---|
| Symbol | SNCA |
| Full Name | Alpha-Synuclein |
| Chromosome | 4q22.1 |
| NCBI Gene | 6622 |
| Ensembl | ENSG00000145335 |
| OMIM | 163890 |
| UniProt | P37840 |
| Diseases | [Parkinson's Disease](/diseases/parkinsons-disease), [Dementia with Lewy Bodies](/diseases/dementia-with-lewy-bodies), [Multiple System Atrophy](/diseases/multiple-system-atrophy) |
| Expression | Substantia nigra, Cerebral [cortex](/brain-regions/cortex), Presynaptic terminals |
| Key Mutations | |
| A53T, A30P, E46K, H50Q, G51D | |
SNCA (Synuclein Alpha) is a gene located on chromosome 4q22.1 that plays a central role in neurodegenerative disease pathogenesis. Mutations and copy number variations in SNCA are causally linked to familial Parkinson's Disease, Dementia with Lewy Bodies, and Multiple System Atrophy 1. The gene is catalogued as NCBI Gene ID 6622 and OMIM 163890.
The protein encoded by SNCA is Alpha-Synuclein (α-Syn), a 140-amino acid protein that is the primary component of Lewy bodies—the hallmark intracellular inclusions found in the brains of patients with Parkinson's disease and related disorders 2. The discovery that α-Syn is the major constituent of Lewy bodies in 1997 revolutionized our understanding of Parkinson's disease pathogenesis and established α-Syn as the focus of intensive therapeutic research.
Alpha-Synuclein is predominantly expressed in presynaptic terminals of neurons, where it comprises up to 1% of total cytosolic protein 3. Under normal physiological conditions, α-Syn plays essential roles in:
α-Syn is expressed throughout the brain but shows highest expression in:
The widespread expression pattern explains why α-Syn pathology affects multiple neurotransmitter systems in Parkinson's disease. Expression data is available from the Allen Human Brain Atlas.
The central pathogenic event in synucleinopathies is the misfolding and aggregation of α-Syn from its native unfolded state into β-sheet-rich oligomers and fibrils. This process involves:
The aggregation is influenced by post-translational modifications including:
A critical breakthrough in understanding Parkinson's disease progression is the discovery that α-Syn can propagate between neurons in a prion-like manner 9:
This mechanism explains the characteristic spread of pathology from the brainstem to cortical regions observed in Braak staging of Parkinson's disease progression 10. According to this staging system, α-Syn pathology first appears in the dorsal motor nucleus and olfactory bulb (stages 1-2), then progresses to the substantia nigra and basal forebrain (stages 3-4), and finally reaches the neocortex (stages 5-6).
See Alpha-Synuclein Prion-Like Spreading Mechanisms and Alpha-Synuclein Propagation Models for detailed pathway information.
The mechanisms by which α-Syn aggregates cause neuronal death include:
SNCA was the first gene linked to familial Parkinson's disease when the A53T mutation was identified in the Contursi kindred in 1997 1. The gene is now recognized as a central player in both familial and sporadic PD:
DLB is characterized by diffuse Lewy body pathology throughout the cortex and limbic system, often coexisting with some amyloid plaques (but minimal tau neurofibrillary tangles). α-Syn aggregates in both Lewy bodies and Lewy neurites 2, and SNCA mutations/duplications contribute to DLB pathogenesis. Clinically, DLB features:
Unlike PD and DLB, MSA features predominantly oligodendroglial inclusion bodies (GCIs) containing α-Syn fibrils 6. This suggests distinct strain properties of α-Syn aggregates in different synucleinopathies. MSA is characterized by:
| Mutation | Location | Effect |
|---|---|---|
| A53T | Residue 53 | Enhanced aggregation, earlier onset (~46 years), severe phenotype |
| A30P | Residue 30 | Reduced membrane binding, enhanced oligomerization |
| E46K | Residue 46 | Increased aggregation, Lewy body formation |
| H50Q | Residue 50 | Moderate aggregation risk, later onset |
| G51D | Residue 51 | Reduced neuronal viability, earlier onset |
The A53T mutation (Ala53Thr) was first described in the Italian Contursi kindred and three Greek families, demonstrating autosomal dominant inheritance with complete penetrance. Transgenic mice expressing human A53T α-Syn develop progressive motor deficits and Lewy body-like inclusions 13.
SNCA promoter polymorphisms (rep1, rep2) influence expression levels, with certain haplotypes associated with increased PD risk. The REP1 microsatellite polymorphism in the SNCA promoter shows the strongest association:
This suggests that increased SNCA expression is a risk factor for idiopathic Parkinson's disease.
Gene duplications and triplications cause autosomal dominant PD with earlier onset and more severe phenotype in triplication cases 13. The first SNCA multiplication was identified in a Swedish family (PARK4), demonstrating that wild-type α-Syn overexpression is sufficient to cause neurodegeneration.
SNCA duplications involve partial or full gene copy number increases on chromosome 4q22.1:
SNCA triplications produce 2-3x normal α-Syn protein levels and cause more severe disease:
The NACP (Non-Amyloid Component of Parkinson's disease, the original name for α-Syn) REP1 microsatellite polymorphism in the SNCA promoter region is a well-established risk modifier[2]:
| REP1 Allele | Length | PD Risk Association |
|---|---|---|
| REP1-263bp | 263 bp | Increased risk (~1.5-2x) |
| REP1-261bp | 261 bp | Neutral/protective |
| REP1-267bp | 267 bp | Variable association |
| REP1-285bp | 285 bp | Increased risk in Asian populations |
Mechanism: The REP1 polymorphism (~7.2 kb upstream of transcription start site) affects transcriptional activity. Risk alleles show higher promoter activity in reporter assays, leading to increased SNCA mRNA expression. Higher α-Syn levels in neurons increase aggregation probability.
Population-specific effects: The 263 bp allele shows strong association in European populations; the 285 bp allele is associated with risk in East Asian cohorts. This explains some of the population variation in SNCA GWAS signals.
Interaction with mutations: REP1 risk alleles can modify the phenotype of SNCA point mutation carriers, with carriers of both REP1 risk allele and A53T having earlier onset than A53T carriers alone.
SNCA is a major therapeutic target for disease modification in synucleinopathies. Multiple strategies are under development:
SNCA-related biomarkers are critical for diagnosis and clinical trials:
Recent studies on alpha-synuclein continue to reveal new mechanisms in Parkinson's disease and related synucleinopathies.
Alpha-synuclein (SNCA) shows high expression in:
Single-cell RNA sequencing data from the Allen Brain Atlas shows SNCA expression in:
| Region | Expression Level | Data Source |
|---|---|---|
| Substantia nigra | High | Human MTG |
| Hippocampus | Medium-High | Mouse Brain |
| Cerebral cortex | Medium | Mouse Brain |
| Cerebellum | Low | Human MTG |
SNCA triplication in Parkinson's disease. Neurobiology of Aging. 2013. ↩︎
Prion-like propagation of alpha-synuclein. Neuron. 2014. ↩︎
Alpha-synuclein strain dynamics correlate with cognitive shifts in Parkinson's disease. Nature Neuroscience. 2026. ↩︎
TMEM106B deficiency exacerbates alpha-synuclein aggregation. Acta Neuropathologica. 2026. ↩︎
Fibrinogen exacerbates alpha-synuclein aggregation via α5β3 integrin. Nature Communications. 2026. ↩︎
Glymphatic system clearance of alpha-synuclein. bioRxiv. 2025. ↩︎
Glucosylceramide-induced ectosomes propagate pathogenic alpha-synuclein. Cell. 2025. ↩︎