What you carry at this position in your DNA and what research says about it.
Crohn's Disease Risk: 8/10 evidence, 51 publications.
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Sample genotype (not yours): C/C
Typical Crohn's and Asthma Risk
Two copies of the standard allele provide normal NOD2 receptor function. This maintains a healthy gut barrier and typical immune responses.
What this genotype means: Typical risk of Crohn's disease; Typical risk of childhood-onset asthma; Normal NOD2 immune receptor function.
Sample genotype (not yours): C/T
Elevated Crohn's and Asthma Risk
Carrying one copy of the variant allele moderately increases the risk of developing Crohn's disease. It also slightly raises susceptibility to childhood-onset asthma and mouth ulcers.
What this genotype means: 2-4x higher risk of Crohn's disease; Slightly increased risk of childhood-onset asthma; Slightly reduced susceptibility to mouth ulcers.
Sample genotype (not yours): T/T
Significantly Higher Crohn's and Asthma Risk
Carrying two copies of the variant allele significantly increases the risk of Crohn's disease. It also elevates the risk of childhood-onset asthma and recurrent mouth ulcers.
What this genotype means: 20-40x higher risk of Crohn's disease; Increased risk of childhood-onset asthma; Lower susceptibility to recurrent mouth ulcers.
Gene function and biological role
Gene Function: The NOD2 gene encodes an intracellular pattern recognition receptor that plays a critical role in the innate immune system [1]. This receptor detects bacterial peptidoglycans, specifically muramyl dipeptide, triggering a protective inflammatory response and promoting autophagy to clear pathogens [1] [2]. Proper function of this gene is essential for maintaining a healthy balance of microbes in the gut and protecting mucosal barriers [2]. When NOD2 signaling is impaired, the body struggles to clear intestinal bacteria, leading to chronic, uncontrolled inflammation [2] [3]. Consequently, variations in this gene are among the most strongly linked genetic factors for inflammatory bowel disorders [3].
Variant Impact: This missense variant, also known as R702W, alters the protein sequence of the NOD2 receptor by replacing the amino acid arginine with tryptophan at position 675. This structural change compromises the receptor's ability to recognize bacterial cell wall components, impairing the normal immune response [1]. Instead of clearing bacteria efficiently, the immune system overcompensates by activating alternative, highly inflammatory pathways [1] [2]. This functional defect significantly increases susceptibility to chronic inflammatory conditions, particularly in the gastrointestinal tract [2]. It also influences systemic immune responses, contributing to inflammatory conditions outside the gut, such as asthma [4].
Key Insight: While this variant is famous for its strong link to Crohn's disease, it also alters systemic immune responses, raising the risk of childhood-onset asthma. Recurrent mouth ulcers run the other way, with the common C allele carrying that risk instead.
Location: NOD2. Chromosome 16 · 16q12.1 · 50.7 Mb
Estimated prevalence by population
Global 94.4%; European 91.2%; African 98.3%; East Asian > 99.9%; South Asian 99.9%; Americas 93.7%; Ashkenazi 96.9%; Finnish 97.1%; Middle Eastern 99.3%; Amish 70.7%.
Estimated CC genotype frequency.
Global 5.4%; European 8.6%; African 1.7%; East Asian < 0.1%; South Asian 0.1%; Americas 6.2%; Ashkenazi 3.1%; Finnish 2.8%; Middle Eastern 0.7%; Amish 26.7%.
Estimated CT genotype frequency.
Global 0.1%; European 0.2%; African < 0.1%; East Asian < 0.1%; South Asian < 0.1%; Americas 0.1%; Ashkenazi < 0.1%; Finnish < 0.1%; Middle Eastern < 0.1%; Amish 2.5%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Immunity & Inflammation
Chronic Inflammatory Diseases
Crohn's Disease. Evidence: 8/10. Source: PMID 11385576. Typical Risk.
Organ Systems
Respiratory Health
Asthma. Evidence: 8/10. Source: PMID 30929738. Typical Risk.
Dental & Oral Health
Mouth Ulcers. Evidence: 8/10. Source: PMID 30837455. Slightly Increased Risk.
Cancer & Oncology
Colorectal Cancer
Colorectal Adenoma. Evidence: 4/10. Source: PMID 29228715. Typical Risk.
Showing effects for C/T genotype
Crohn's Disease. Evidence: 8/10. Source: PMID 11385576. ~2-4x Increased Risk.
Asthma. Evidence: 8/10. Source: PMID 30929738. Slightly Increased.
Mouth Ulcers. Evidence: 8/10. Source: PMID 30837455. Slightly Reduced Risk.
Colorectal Adenoma. Evidence: 4/10. Source: PMID 29228715. Slightly Increased.
Showing effects for T/T genotype
Crohn's Disease. Evidence: 8/10. Source: PMID 11385576. ~20-40x Increased Risk.
Asthma. Evidence: 8/10. Source: PMID 30929738. Increased Risk.
Mouth Ulcers. Evidence: 8/10. Source: PMID 30837455. Reduced Risk.
Colorectal Adenoma. Evidence: 4/10. Source: PMID 29228715. Increased Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Having two copies of the reference C allele ensures the NOD2 receptor maintains its normal structure and function [1]. The immune system can successfully recognize bacterial cell wall components in the gut, keeping the intestinal microbiome balanced and preventing chronic inflammation [1] [2]. Studies show that this typical genotype does not elevate the risk for Crohn's disease or other forms of inflammatory bowel disease [2] [3]. It is associated with a baseline, typical risk for childhood-onset asthma [4]. Recurrent mouth ulcers are the one trait here that runs the other way: the common C allele is the one that raises them, so this genotype carries a slightly higher chance [5]. Maintaining a balanced diet rich in fiber and supporting gut health remains beneficial for overall wellness. This genotype represents the most common genetic profile globally.
Typical risk of Crohn's disease; Typical risk of childhood-onset asthma; Normal NOD2 immune receptor function; Slightly higher chance of recurrent mouth ulcers.
Sample genotype: CT (Heterozygous)
Carrying one copy of the T allele alters a portion of the NOD2 receptors, moderately reducing the body's ability to detect and clear gut bacteria [1]. This immune impairment is linked to a roughly two- to four-fold increase in the risk of developing Crohn's disease [1] [2]. Research also associates this genotype with a slightly higher susceptibility to childhood-onset asthma, driven by altered systemic immune pathways [3] [4]. Recurrent mouth ulcers run the opposite way at this variant, where the T allele is the protective one, so this genotype carries a slightly lower chance of them [5]. While this profile increases susceptibility, many individuals with this genotype never develop inflammatory bowel disease. Focusing on gut-friendly lifestyle choices and avoiding smoking can help manage overall inflammatory risks.
2-4x higher risk of Crohn's disease; Slightly increased risk of childhood-onset asthma; Slightly reduced susceptibility to mouth ulcers.
Sample genotype: TT (Homozygous)
Carrying two copies of the T allele severely compromises the function of the NOD2 receptor, leading to a profound defect in bacterial sensing within the gut [1]. This functional loss is strongly associated with a twenty- to forty-fold increase in the risk of developing Crohn's disease [1] [2]. The chronic lack of proper bacterial clearance triggers severe, persistent inflammation along the digestive tract [2] [3]. Beyond the gut, this genotype is linked to a significantly higher risk of childhood-onset asthma due to systemic immune dysregulation [4] [5]. Recurrent mouth ulcers are actually less common with this genotype, the one trait at this variant where the T allele is protective rather than harmful [6]. Although the genetic risk is high, environmental factors play a major role in whether symptoms actually manifest. Proactive gut health management and regular medical consultations are highly recommended.
20-40x higher risk of Crohn's disease; Increased risk of childhood-onset asthma; Lower susceptibility to recurrent mouth ulcers.
Variants with shared genetic architecture
rs2066845 · NOD2 Gene · Chr 16 · Crohn's Disease Risk
rs2076756 · NOD2 Gene · Chr 16 · Crohn's Disease Risk
rs2066847 · NOD2 Gene · Chr 16 · Crohn's Disease Risk
Association of NOD2 leucine-rich repeat variants with susceptibility to Crohn's disease.
A frameshift mutation in NOD2 associated with susceptibility to Crohn's disease.
Genetic Architectures of Childhood- and Adult-Onset Asthma Are Partly Distinct.
Genome wide analysis for mouth ulcers identifies associations at immune regulatory loci.
Content updated August 2026.
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