SNCA rs2736990 — The Intron 4 Variant
The SNCA gene11 SNCA gene
Alpha-synuclein (SNCA) encodes the protein that aggregates into Lewy bodies — the pathological hallmark of Parkinson's disease and related synucleinopathies harbors multiple independent risk variants, each tagging different biological mechanisms at the same locus. rs2736990 sits within intron 4 of SNCA — a region known for a complex CT-rich haplotype structure that influences alpha-synuclein expression and splicing22 complex CT-rich haplotype structure that influences alpha-synuclein expression and splicing — and was the first intronic SNCA variant to reach genome-wide significance in a large European GWAS.
The Mechanism
rs2736990 is classified as an intronic variant33 intronic variant
A variant located within a non-coding region of a gene (intron); intronic variants can influence gene expression, splicing efficiency, or RNA stability without changing the protein sequence in intron 4 of SNCA. The precise molecular mechanism by which this variant alters disease risk is not fully established, but the leading hypothesis is that it influences SNCA pre-mRNA splicing or expression levels.
The Evidence
The discovery of rs2736990 as a Parkinson's disease risk variant came from a landmark 2009 European genome-wide association study44 a landmark 2009 European genome-wide association study
Simón-Sánchez et al. Genome-wide association study reveals genetic risk underlying Parkinson's disease. Nature Genetics, 2009 that enrolled 1,713 cases and 3,978 controls, with replication in an independent cohort of 3,361 cases and 4,573 controls. The SNCA signal at rs2736990 was one of the two strongest associations identified, with OR 1.23 and p=2.24×10⁻¹⁶ — a highly robust association by GWAS standards.
A Chinese Han case-control study55 A Chinese Han case-control study
Association of polymorphism in rs2736990 of the α-synuclein gene with Parkinson's disease in a Chinese population. Neurology India, 2013 (515 PD patients, 450 controls) confirmed the C allele as a PD risk factor (OR 1.26, 95% CI 1.04–1.51; p=0.017) and identified a stronger effect in early-onset patients diagnosed at or before age 50 (OR 1.60, 95% CI 1.13–2.26; p=0.007). This early-onset enrichment is clinically significant — it suggests that among younger PD patients, rs2736990 is playing a more prominent etiological role.
A 2017 meta-analysis66 2017 meta-analysis
Association between SNCA rs2736990 polymorphism and Parkinson's disease: a meta-analysis. Neuroscience Letters, 2017 pooling six studies (2,525 PD cases, 2,165 controls) formally established the risk direction: the C allele (G on plus strand) confers increased risk, with an allele model OR of 1.30. Under the recessive model (CC vs TT+TC), the OR for the homozygous risk genotype was 1.52.
The 2017 Brazilian cohort77 2017 Brazilian cohort
Campelo et al. Variants in SNCA Gene Are Associated with Parkinson's Disease Risk and Cognitive Symptoms in a Brazilian Sample. Frontiers in Aging Neuroscience, 2017 (104 PD patients, 98 controls) provided crucial data linking rs2736990 directly to cognitive outcomes. The CC homozygous genotype was associated with OR 2.65 (95% CI 1.13–6.20) for PD overall, and the C allele was significantly more frequent among PD patients with cognitive impairment (70%) versus controls (52%), yielding OR 2.21 (95% CI 1.26–3.85; p=0.005). The C allele also associated with early-onset PD (OR 1.88, 95% CI 1.07–3.29; p=0.028).
The largest systematic assessment comes from a 2018 comprehensive meta-analysis88 2018 comprehensive meta-analysis
A Comprehensive Analysis of the Association Between SNCA Polymorphisms and the Risk of Parkinson's Disease. Frontiers in Molecular Neuroscience, 2018 covering 24,075 cases and 22,877 controls across 36 studies. Among 16 SNCA variants analyzed, rs2736990 was classified as one of eight "most recommended" variants (p<1×10⁻⁵) for genetic risk assessment, with OR 1.22 in the allele model (95% CI 1.13–1.31) and OR 1.30 in both dominant and recessive models. The G allele frequency in unaffected controls was 0.56 globally and 0.62 in East Asian controls, confirming the variant is common — not a rare pathogenic mutation, but a frequent risk-modifying variant.
Practical Actions
For G-allele carriers who are younger or have a family history of PD, establishing a neurological baseline and monitoring for early prodromal signs (hyposmia, REM sleep behavior disorder, constipation, subtle motor asymmetry) is particularly valuable given this variant's association with earlier onset.