What you carry at this position in your DNA and what research says about it.
Macular Degeneration Risk: 9/10 evidence, 37 publications.
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Sample genotype (not yours): C/C
Typical Vision Risk but Higher Hypothyroidism Risk
A typical risk of macular degeneration is paired with a slightly elevated risk of developing hypothyroidism. This genotype also offers a lower risk of aspirin-induced asthma.
What this genotype means: Typical risk of dry age-related macular degeneration; Slightly higher risk of hypothyroidism; Lower risk of aspirin-induced asthma.
Sample genotype (not yours): C/T
Lower Macular Degeneration Risk but Higher Asthma Risk
One copy of the variant allele reduces the risk of dry age-related macular degeneration. However, it is linked to an increased risk of aspirin-induced asthma.
What this genotype means: ~30% lower risk of dry age-related macular degeneration; Increased risk of aspirin-induced asthma; Slightly weaker response to measles vaccination.
Sample genotype (not yours): T/T
Lowest Macular Degeneration Risk but Higher Asthma Risk
Two copies of the variant allele significantly lower the risk of dry age-related macular degeneration and hypothyroidism. However, they increase the risk of aspirin-induced asthma.
What this genotype means: ~56% lower risk of dry age-related macular degeneration; Slightly lower risk of hypothyroidism; Increased risk of aspirin-induced asthma.
Gene function and biological role
Gene Function: The TLR3 gene encodes Toll-like receptor 3, a vital component of the innate immune system [1]. This receptor specializes in detecting double-stranded RNA, which is a common signature of viral replication [1]. Upon activation, it triggers signaling cascades that produce interferon and other inflammatory cytokines to fight infections [1]. Beyond viral defense, its inflammatory signaling is implicated in chronic conditions like macular degeneration and autoimmune thyroid disease [2]. Proper regulation of this receptor is essential for maintaining tissue homeostasis and preventing autoimmune destruction [2].
Variant Impact: The rs3775291 variant is a missense mutation in the TLR3 gene that alters the receptor's structure [3]. This genetic change substitutes the amino acid leucine with phenylalanine at position 412 of the protein [3]. The alteration reduces the receptor's signaling activity and its binding capacity for double-stranded RNA [3]. Consequently, this functional dampening leads to decreased inflammatory cell death in the retina, protecting against macular degeneration [3]. However, the same reduction in immune signaling can alter susceptibility to autoimmune thyroid conditions and affect vaccine responses [4].
Key Insight: A genetic variant that dampens your immune response actually protects your vision by preventing inflammatory cell death in the retina.
Location: TLR3. Chromosome 4 · 4q35.1 · 186.1 Mb
Estimated prevalence by population
Global 59.5%; European 49.3%; African 86.7%; East Asian 45.9%; South Asian 56.9%; Americas 47.1%; Ashkenazi 56.5%; Finnish 45.8%; Middle Eastern 60.7%; Amish 53.6%.
Estimated CC genotype frequency.
Global 33.9%; European 41.9%; African 12.9%; East Asian 43.7%; South Asian 37.1%; Americas 43.1%; Ashkenazi 37.4%; Finnish 43.8%; Middle Eastern 34.4%; Amish 39.2%.
Estimated CT genotype frequency.
Global 6.7%; European 8.9%; African 0.5%; East Asian 10.4%; South Asian 6.0%; Americas 9.9%; Ashkenazi 6.2%; Finnish 10.5%; Middle Eastern 4.9%; Amish 7.2%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Organ Systems
Vision & Eye Health
Macular Degeneration. Evidence: 4/10. Source: PMID 18385087. Typical Risk.
Endocrine & Reproductive
Hormone Levels & Endocrine Regulation
Hypothyroidism. Evidence: 9/10. Source: PMID 34594039. Slightly Higher Risk.
Pharmacogenomics
Adverse Drug Reactions
Aspirin-Induced Asthma. Evidence: 5/10. Source: PMID 21461252. Typical Risk.
Immunity & Inflammation
Infection Susceptibility & Resistance
Measles Vaccine Response. Evidence: 5/10. Source: PMID 18325643. Typical Response.
Showing effects for C/T genotype
Macular Degeneration. Evidence: 4/10. Source: PMID 18385087. ~30% Lower Risk.
Hypothyroidism. Evidence: 9/10. Source: PMID 34594039. Typical Risk.
Aspirin-Induced Asthma. Evidence: 5/10. Source: PMID 21461252. Increased Risk.
Measles Vaccine Response. Evidence: 5/10. Source: PMID 18325643. Poorer Response.
Showing effects for T/T genotype
Macular Degeneration. Evidence: 4/10. Source: PMID 18385087. ~56% Lower Risk.
Hypothyroidism. Evidence: 9/10. Source: PMID 34594039. Slightly Lower Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
A baseline risk of age-related macular degeneration is associated with the common CC genotype [1]. Retinal pigment epithelial cells with this genotype are more susceptible to double-stranded RNA-induced cell death [1]. Additionally, this genotype is linked to a slightly higher risk of developing hypothyroidism and requiring thyroid medication [2]. However, individuals with this genotype have a lower risk of developing aspirin-intolerant asthma [3]. They also exhibit a typical, robust immune response to the measles vaccine [4].
Typical risk of dry age-related macular degeneration; Slightly higher risk of hypothyroidism; Lower risk of aspirin-induced asthma.
Sample genotype: CT (Heterozygous)
Protection against dry age-related macular degeneration is moderately increased by the presence of one T allele [1]. This protective effect is thought to stem from reduced receptor activity, which limits inflammatory cell death in the retina [1]. However, this genotype is associated with a slightly increased risk of aspirin-intolerant asthma [2]. It is also linked to a poorer antibody response following measles vaccination [3]. On the other hand, this genotype is associated with a typical risk of hypothyroidism, avoiding the slightly elevated risk seen in the common genotype [4].
~30% lower risk of dry age-related macular degeneration; Increased risk of aspirin-induced asthma; Slightly weaker response to measles vaccination.
Sample genotype: TT (Homozygous)
A significant reduction in the risk of dry age-related macular degeneration is experienced by those with two copies of the T allele [1]. The structural change in the receptor reduces inflammatory cell death in retinal cells, preserving vision [1]. This genotype also offers protection against hypothyroidism and autoimmune thyroid disease [2]. However, these benefits are accompanied by an increased risk of developing aspirin-intolerant asthma [3].
~56% lower risk of dry age-related macular degeneration; Slightly lower risk of hypothyroidism; Increased risk of aspirin-induced asthma.
Variants with shared genetic architecture
rs3775290 · TLR3 Gene · Chr 4 · Osteoarthritis Risk
rs10468017 · LIPC Gene · Chr 15 · Cholesterol and Eye Health
rs10490924 · ARMS2 Gene · Chr 10 · Macular Degeneration Risk
FLT3 stop mutation increases FLT3 ligand level and risk of autoimmune thyroid disease.
Toll-like receptor polymorphisms and age-related macular degeneration.
Genome-wide association study of medication-use and associated disease in the UK Biobank.
Role of Toll-like Receptor 3 Variants in Aspirin-Exacerbated Respiratory Disease.
A cross-population atlas of genetic associations for 220 human phenotypes.
Content updated August 2026.
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