What you carry at this position in your DNA and what research says about it.
Lupus and Autoimmune Risk: 6/10 evidence, 47 publications.
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Sample genotype (not yours): C/C
Lower Lupus Risk but Higher Anxiety Susceptibility
Carrying two copies of the C allele provides protection against systemic lupus erythematosus but is linked to higher anxiety levels.
What this genotype means: Lower risk of systemic lupus erythematosus; Higher susceptibility to anxiety; Typical risk of Parkinson's disease.
Sample genotype (not yours): C/T
Increased Lupus Risk with Lower Parkinson's Risk
Carrying one copy of the T allele increases susceptibility to lupus but offers protection against Parkinson's disease.
What this genotype means: Increased risk of systemic lupus erythematosus; Lower risk of Parkinson's disease; Slightly higher cognitive function.
Sample genotype (not yours): T/T
Higher Lupus Risk with Lower Parkinson's and Anxiety Risk
Carrying two copies of the T allele elevates lupus susceptibility but protects against Parkinson's disease and anxiety.
What this genotype means: Increased risk of systemic lupus erythematosus; Lower risk of Parkinson's disease; Lower susceptibility to anxiety.
Gene function and biological role
Gene Function: The TLR9 gene encodes toll-like receptor 9, a critical component of the innate immune system. This receptor is primarily expressed in immune cells such as dendritic cells and B lymphocytes, where it detects foreign viral and bacterial DNA. By recognizing these pathogen-associated molecular patterns, the receptor triggers inflammatory cytokine production and coordinates defensive immune responses. However, overactivation or dysregulation of this pathway can lead the immune system to mistakenly target the body's own tissues, contributing to autoimmune conditions [1]. It also plays a role in neuroinflammation and systemic inflammatory pathways linked to neurological health [2].
Variant Impact: The rs352140 variant is a synonymous single nucleotide polymorphism located in exon 2 of the TLR9 gene. Although it does not alter the amino acid sequence of the protein, this genetic change is functional and influences TLR9 gene expression levels. The T allele is associated with higher expression of TLR9 mRNA in B cells, which can enhance immune reactivity. This increased expression can heighten the risk of autoimmune flare-ups while simultaneously altering susceptibility to certain neurodegenerative and infectious diseases. The variant is widely studied across diverse global populations for its pleiotropic effects on immunity and behavior.
Key Insight: This genetic variant presents a classic evolutionary trade-off where alleles that increase the risk of autoimmune diseases like lupus simultaneously offer protection against Parkinson's disease.
Location: TLR9. Chromosome 3 · 3p21.2 · 52.2 Mb
Estimated prevalence by population
Global 29.3%; European 21.3%; African 44.6%; East Asian 37.7%; South Asian 33.8%; Americas 24.2%; Ashkenazi 20.3%; Finnish 27.3%; Middle Eastern 23.3%; Amish 15.0%.
Estimated CC genotype frequency.
Global 48.2%; European 49.7%; African 44.4%; East Asian 47.4%; South Asian 48.7%; Americas 50.0%; Ashkenazi 49.5%; Finnish 49.9%; Middle Eastern 49.9%; Amish 47.5%.
Estimated CT genotype frequency.
Global 22.5%; European 29.0%; African 11.0%; East Asian 14.9%; South Asian 17.5%; Americas 25.8%; Ashkenazi 30.2%; Finnish 22.8%; Middle Eastern 26.7%; Amish 37.5%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Immunity & Inflammation
Autoimmune Diseases
Lupus. Evidence: 4/10. Source: PMID 22948541. Typical Risk.
Neurology & Mental Health
Neurodegenerative Diseases
Parkinson's Disease. Evidence: 3/10. Source: PMID 33382388. Typical Risk.
Anxiety & Stress Disorders
Anxiety. Evidence: 6/10. Source: PMID 29942085. Increased Risk.
Cognitive Performance
Cognitive Function. Evidence: 6/10. Source: PMID 40374629. Typical.
Showing effects for C/T genotype
Lupus. Evidence: 4/10. Source: PMID 22948541. Increased Risk.
Parkinson's Disease. Evidence: 3/10. Source: PMID 33382388. Lower Risk.
Cognitive Function. Evidence: 6/10. Source: PMID 40374629. Slightly Higher.
Showing effects for T/T genotype
Anxiety. Evidence: 6/10. Source: PMID 29942085. Typical Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Inheriting the C/C genotype is associated with a lower risk of developing systemic lupus erythematosus and lupus nephritis compared to T allele carriers [1]. This protective effect is likely due to lower baseline expression of the TLR9 receptor, which reduces the likelihood of the immune system overreacting to self-DNA. However, this genotype is associated with an increased susceptibility to anxiety and neuroticism, as identified in large-scale genome-wide association studies [2]. Additionally, individuals with this genotype exhibit typical cognitive function and do not benefit from the protective effect against Parkinson's disease seen in T allele carriers [3]. Maintaining a balanced lifestyle with stress-reduction techniques can help manage potential anxiety risks.
Lower risk of systemic lupus erythematosus; Higher susceptibility to anxiety; Typical risk of Parkinson's disease.
Sample genotype: CT (Heterozygous)
Possessing the C/T genotype represents a complex genetic trade-off between autoimmune susceptibility and neurological protection. Clinical studies indicate that carrying a T allele increases the risk of systemic lupus erythematosus and associated renal complications like lupus nephritis [1]. This risk is driven by higher TLR9 receptor expression, which can amplify autoimmune inflammatory cascades. Conversely, this same immune activity appears to be protective in the brain, where the T allele is linked to a significantly lower risk of developing Parkinson's disease [2]. Additionally, this genotype is associated with slightly higher cognitive function and a typical baseline for anxiety [3]. Managing systemic inflammation through diet and exercise may help mitigate autoimmune risks while preserving neurological benefits.
Increased risk of systemic lupus erythematosus; Lower risk of Parkinson's disease; Slightly higher cognitive function.
Sample genotype: TT (Homozygous)
Having the T/T genotype presents a pronounced genetic trade-off across multiple body systems. This genotype is significantly associated with an increased susceptibility to systemic lupus erythematosus and the development of anti-dsDNA antibodies [1]. The elevated TLR9 expression characteristic of this genotype can drive autoimmune responses. However, this active immune profile is highly protective against neurodegeneration, correlating with a reduced risk of Parkinson's disease [2]. Furthermore, genome-wide studies link this genotype to lower anxiety susceptibility and improved cognitive performance over time [3]. Regular medical checkups can help monitor for early signs of autoimmunity, allowing you to benefit from your natural neurological advantages.
Increased risk of systemic lupus erythematosus; Lower risk of Parkinson's disease; Lower susceptibility to anxiety.
Variants with shared genetic architecture
rs187084 · TLR9 Gene · Chr 3 · Autoimmune and Obesity Risk
rs352139 · TLR9 Gene · Chr 3 · Immune Defense and Gut Health
rs5743836 · TLR9 Gene · Chr 3 · Immune System Activity
Content updated August 2026.
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