What you carry at this position in your DNA and what research says about it.
Autoimmune Disease Risk: 8/10 evidence, 41 publications.
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Sample genotype (not yours): T/T
Increased Risk of Autoimmune Diseases
Two copies of the T allele are associated with a higher susceptibility to several autoimmune conditions. This genetic profile is linked to an increased risk of type 1 diabetes, multiple sclerosis, and rheumatoid arthritis.
What this genotype means: Higher risk of type 1 diabetes; Higher risk of multiple sclerosis; Slightly higher risk of rheumatoid arthritis.
Sample genotype (not yours): C/C
Typical Risk of Autoimmune Diseases
Two copies of the C allele are associated with a typical or baseline risk for multiple autoimmune conditions. This genotype does not carry the hyperactive immune receptor variant.
What this genotype means: Typical baseline risk for type 1 diabetes; Typical baseline risk for multiple sclerosis; Typical baseline risk for rheumatoid arthritis.
Sample genotype (not yours): T/C
Slightly Increased Risk of Autoimmune Diseases
One copy of the T allele is linked to a slightly elevated risk of developing various autoimmune conditions. This intermediate profile sits between the higher-risk T/T and typical-risk C/C genotypes.
What this genotype means: Slightly higher risk of type 1 diabetes; Slightly higher risk of multiple sclerosis; Minor increase in rheumatoid arthritis risk.
Gene function and biological role
Gene Function: The CD226 gene encodes a cell surface glycoprotein, also known as DNAM-1, which is expressed on T cells, natural killer cells, and other immune cells [1]. This receptor acts as a co-stimulatory molecule that promotes the activation, proliferation, and inflammatory activity of immune cells [2]. It plays a critical role in the balance between immune activation and regulation, helping the body fight off pathogens [2]. However, altered activity of CD226 can disrupt this balance, leading the immune system to mistakenly attack the body's own tissues [2].
Variant Impact: A single nucleotide change in the CD226 gene, rs763361, results in a missense mutation that alters the protein structure [2]. This alteration replaces the amino acid glycine with serine at position 307 of the receptor [1]. The change is located in a critical intracellular region of the receptor, which is involved in transmitting activation signals [1]. The serine-encoding T allele is thought to result in a more active form of the CD226 receptor [2].
Key Insight: A single amino acid change in the CD226 receptor can alter immune cell signaling enough to influence susceptibility to multiple distinct autoimmune conditions simultaneously.
Location: CD226. Chromosome 18 · 18q22.2 · 69.9 Mb
Estimated prevalence by population
Global 29.0%; European 22.4%; African 48.6%; East Asian 12.9%; South Asian 25.9%; Americas 20.9%; Ashkenazi 20.2%; Finnish 18.4%; Middle Eastern 40.0%; Amish 32.4%.
Estimated TT genotype frequency.
Global 47.5%; European 49.9%; African 42.2%; East Asian 46.0%; South Asian 50.0%; Americas 49.6%; Ashkenazi 49.5%; Finnish 49.0%; Middle Eastern 46.5%; Amish 49.0%.
Estimated TC genotype frequency.
Global 23.4%; European 27.8%; African 9.2%; East Asian 41.1%; South Asian 24.2%; Americas 29.4%; Ashkenazi 30.3%; Finnish 32.6%; Middle Eastern 13.5%; Amish 18.6%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Immunity & Inflammation
Autoimmune Diseases
Autoimmune Disease Risk. Evidence: 8/10. Source: PMID 20338887. Increased Risk.
Multiple Sclerosis. Evidence: 4/10. Source: PMID 30128676. Increased Risk.
Rheumatoid Arthritis. Evidence: 4/10. Source: PMID 25645050. Increased Risk.
Cardiovascular & Metabolic
Diabetes & Glycemic Traits
Type 1 Diabetes. Evidence: 7/10. Source: PMID 17554260. Increased Risk.
Blood Cell & Iron Traits
Reticulocyte Count. Evidence: 8/10. Source: PMID 39789286. Slightly Higher.
Lifestyle, Fitness & Aging
Height & Body Size
Height. Evidence: 7/10. Source: PMID 36224396. Slightly Shorter.
Showing effects for C/C genotype
Autoimmune Disease Risk. Evidence: 8/10. Source: PMID 20338887. Typical Risk.
Multiple Sclerosis. Evidence: 4/10. Source: PMID 30128676. Typical Risk.
Rheumatoid Arthritis. Evidence: 4/10. Source: PMID 25645050. Typical Risk.
Type 1 Diabetes. Evidence: 7/10. Source: PMID 17554260. Typical Risk.
Reticulocyte Count. Evidence: 8/10. Source: PMID 39789286. Slightly Lower.
Height. Evidence: 7/10. Source: PMID 36224396. Slightly Taller.
Showing effects for T/C genotype
Autoimmune Disease Risk. Evidence: 8/10. Source: PMID 20338887. Slightly Increased.
Multiple Sclerosis. Evidence: 4/10. Source: PMID 30128676. Slightly Increased.
Rheumatoid Arthritis. Evidence: 4/10. Source: PMID 25645050. Slightly Increased.
Type 1 Diabetes. Evidence: 7/10. Source: PMID 17554260. Slightly Increased.
Reticulocyte Count. Evidence: 8/10. Source: PMID 39789286. Typical.
Height. Evidence: 7/10. Source: PMID 36224396. Typical Height.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Serine at position 307 of the CD226 receptor, encoded by the T/T genotype, represents the risk-associated form of this immune molecule [1]. This variant leads to hyperactive immune signaling, making T cells more prone to attacking healthy tissues [2]. Large-scale genetic studies have consistently linked this genotype to an increased risk of developing type 1 diabetes [3]. It is also strongly associated with multiple sclerosis susceptibility across diverse populations [4]. Additionally, carriers of this genotype have an elevated risk of other autoimmune conditions, such as rheumatoid arthritis and systemic sclerosis [5]. While this genetic profile increases susceptibility, it is not a direct diagnosis, as environmental factors play a major role in whether an autoimmune disease actually develops [6].
Higher risk of type 1 diabetes; Higher risk of multiple sclerosis; Slightly higher risk of rheumatoid arthritis.
Sample genotype: CC (Homozygous)
Glycine at position 307 of the CD226 receptor, encoded by the C/C genotype, represents the protective or typical form of this immune molecule [1]. This version of the receptor maintains balanced immune signaling, avoiding the hyperactivation seen with the T allele [2]. As a result, individuals with this genotype have a normal, baseline risk for developing type 1 diabetes [3]. They also do not carry the elevated genetic risk for multiple sclerosis associated with this locus [4]. Furthermore, studies show a typical risk profile for other autoimmune conditions, including rheumatoid arthritis and systemic lupus erythematosus [5]. While this genotype is protective against the elevated risks of the T allele, it does not make a person completely immune to autoimmune diseases, as other genetic and environmental factors still contribute [6].
Typical baseline risk for type 1 diabetes; Typical baseline risk for multiple sclerosis; Typical baseline risk for rheumatoid arthritis.
Sample genotype: TC (Heterozygous)
A heterozygous T/C profile means one copy of the CD226 gene encodes serine and the other encodes glycine [1]. This heterozygous state results in a mixture of typical and hyperactive CD226 receptors on the surface of immune cells [2]. Consequently, carriers have a slightly elevated susceptibility to autoimmune disorders compared to those with the C/C genotype [3]. Research has shown a modest increase in the risk of type 1 diabetes and multiple sclerosis for individuals with this genetic profile [4]. It is also associated with a minor increase in susceptibility to rheumatoid arthritis and systemic lupus erythematosus [5]. Because autoimmune diseases are complex and multifactorial, lifestyle and environmental triggers remain critical components of overall risk [6].
Slightly higher risk of type 1 diabetes; Slightly higher risk of multiple sclerosis; Minor increase in rheumatoid arthritis risk.
Variants with shared genetic architecture
rs3129934 · TSBP1 Gene · Chr 6 · Multiple Sclerosis Risk
rs1077667 · TNFSF14 Gene · Chr 19 · Multiple Sclerosis Risk
rs1800693 · TNFRSF1A Gene · Chr 12 · Multiple Sclerosis Risk
Robust associations of four new chromosome regions from genome-wide analyses of type 1 diabetes.
CD226 Gly307Ser association with multiple autoimmune diseases: a meta-analysis.
Association of CD226 polymorphisms with the susceptibility to type 1 diabetes in Chinese children.
Content updated August 2026.
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