rs2066845 — NOD2 G908R

NOD2 bacterial sensor variant that increases Crohn's disease risk by impairing immune response to gut bacteria

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NOD2 G908R — A Key Bacterial Sensor Variant in Crohn's Disease

The NOD2 gene encodes an intracellular pattern recognition receptor that detects bacterial cell wall fragments11 detects bacterial cell wall fragments
NOD2 specifically recognizes muramyl dipeptide (MDP), a conserved component found in peptidoglycan from both Gram-positive and Gram-negative bacteria. When bacteria are present, NOD2 triggers immune responses through the NF-κB pathway, producing antimicrobial peptides and recruiting immune cells to fight infection. The G908R variant (rs2066845), one of the three major Crohn's disease-associated NOD2 mutations, substitutes glycine with arginine at amino acid position 90822 substitutes glycine with arginine at amino acid position 908
This missense mutation occurs in the leucine-rich repeat (LRR) domain, the bacterial-sensing region of the NOD2 protein, impairing its ability to detect bacterial signals.

The Mechanism

NOD2 is primarily expressed in intestinal epithelial cells and immune cells33 primarily expressed in intestinal epithelial cells and immune cells
Particularly concentrated in Paneth cells of the small intestine, which secrete antimicrobial compounds to control gut bacteria. When functioning normally, NOD2 detects muramyl dipeptide from bacterial cell walls and activates the NF-κB signaling cascade, leading to production of inflammatory cytokines and alpha-defensins—powerful antimicrobial peptides that keep bacterial populations in check. The G908R mutation disrupts this process: the amino acid change in the bacterial-sensing LRR domain reduces NOD2's ability to bind muramyl dipeptide44 reduces NOD2's ability to bind muramyl dipeptide
Studies show G908R shares a common signaling defect with other CD-associated NOD2 variants, exhibiting impaired NF-κB activation in response to bacterial components. This leads to decreased production of antimicrobial peptides, allowing bacterial populations to grow unchecked and potentially triggering chronic inflammation.

The Evidence

G908R is one of three NOD2 variants strongly associated with Crohn's disease55 G908R is one of three NOD2 variants strongly associated with Crohn's disease
First identified in 2001, these variants account for over 80% of NOD2-associated Crohn's disease cases. The variant's impact follows a clear dose-response pattern: a comprehensive meta-analysis of 75 case-control studies66 a comprehensive meta-analysis of 75 case-control studies
Included 18,727 Crohn's disease cases and 17,102 controls across multiple populations found odds ratios of 2.6 for simple heterozygotes, 9.0 for compound heterozygotes (carrying two different NOD2 mutations), and 6.7 for homozygotes compared to non-carriers. The effect is most pronounced for ileal Crohn's disease—the form affecting the small intestine—where NOD2 mutations confer 2-3 fold increased risk with one copy, and up to 9-fold with two different NOD2 mutations77 NOD2 mutations confer 2-3 fold increased risk with one copy, and up to 9-fold with two different NOD2 mutations.

G908R carriers show specific disease characteristics88 G908R carriers show specific disease characteristics
A retrospective study of 202 Crohn's disease patients found G908R heterozygosity associated with ileal involvement and smoking. A 2025 clinical review99 2025 clinical review
Synthesizing evidence on NOD2 genotype-phenotype correlations in CD management confirmed that NOD2 mutations predict surgical risk, with the strongest effect in L1007fs carriers, though all three variants including G908R contribute to complicated disease course and treatment planning decisions. The variant also affects the gut microbiome: NOD2-deficient mice show altered commensal microbial composition1010 NOD2-deficient mice show altered commensal microbial composition
with increased bacterial loads and shifts in Firmicutes-to-Bacteroidetes ratio in the terminal ileum, suggesting the genetic variant alters microbiome composition even before inflammation appears.

Practical Implications

Knowing your G908R status provides actionable information about gut health and disease risk. For carriers, the impaired bacterial sensing1111 impaired bacterial sensing
NOD2-deficient mice show increased bacterial loads and reduced ability to prevent pathogenic bacterial colonization means extra attention to gut microbiome health is warranted. Unlike some genetic risk factors, NOD2 variants don't doom you to disease—only 30-40% of Crohn's disease patients carry at least one NOD2 mutation1212 only 30-40% of Crohn's disease patients carry at least one NOD2 mutation
Conversely, 6-7% of healthy controls carry these mutations without developing disease, highlighting the importance of environmental and microbial factors.

For those with Crohn's disease who carry G908R, the variant has clinical implications: it predicts ileal location1313 ileal location
The terminal ileum, where Paneth cells are concentrated and NOD2 is most highly expressed, more aggressive disease course, and increased risk of needing surgery. This information can guide treatment decisions, with some evidence suggesting NOD2 mutation carriers may benefit more from early aggressive therapy to prevent complications.

Interactions

G908R frequently co-occurs with other NOD2 variants in compound heterozygous states, which dramatically amplifies risk. The most clinically significant combinations involve G908R with R702W (rs2066844) or with the L1007fs frameshift mutation (rs2066847). When someone carries two different NOD2 risk variants—one from each parent—the odds ratio for Crohn's disease jumps to 9.0, compared to 2.2 for a single variant. This multiplicative effect suggests the variants work through the same pathway, with each defective copy further impairing bacterial sensing.

Beyond NOD2 itself, G908R interacts with variants in genes involved in autophagy—the cellular process that digests intracellular bacteria. The ATG16L1 variant (rs2241880) is particularly relevant: NOD2 recruits ATG16L1 to bacterial entry sites1414 NOD2 recruits ATG16L1 to bacterial entry sites
This interaction is crucial for packaging invaded bacteria into autophagosomes for destruction. When both NOD2 and ATG16L1 are defective, bacterial clearance is severely compromised, potentially explaining why some NOD2 carriers develop disease while others don't. Studies of double-deficient mice show they develop spontaneous intestinal inflammation only when specific bacteria like Mucispirillum schaedleri are present, reinforcing that disease requires both genetic susceptibility and microbial triggers.

Genotype Interpretations

What each possible genotype means for this variant.

GG Normal

Normal NOD2 bacterial sensing function

You carry two normal copies of the NOD2 gene at this position, giving you full bacterial sensing capability. Your NOD2 proteins efficiently detect bacterial cell wall fragments (muramyl dipeptide) in your gut, triggering appropriate immune responses and antimicrobial peptide production. This genotype is found in about 98% of people of European descent. Your baseline genetic risk for Crohn's disease from this specific variant is not elevated, though other NOD2 variants (R702W, L1007fs) or genes may still influence your risk.

CG Moderately Impaired Sensor Intermediate

One copy of G908R moderately increases Crohn's disease risk

As a heterozygote, you have one functioning and one mutant copy of NOD2 at each cell. This provides partial protection—your functional allele still produces working NOD2 proteins that can detect bacterial peptidoglycan and mount appropriate immune responses. However, the 50% reduction in functional NOD2 is enough to detectably alter bacterial-host interactions. Studies show heterozygous carriers have measurable increases in certain bacterial families in their stool, suggesting the defect affects microbiome composition. The G908R heterozygous state shows particular association with ileal Crohn's involvement and has also been linked to smoking as a synergistic risk factor. Importantly, compound heterozygosity—carrying G908R plus a different NOD2 mutation like R702W or L1007fs—dramatically increases risk (OR 9.0), so knowing your full NOD2 genotype status matters if multiple variants run in your family.

CC Impaired Bacterial Sensor Homozygous

Two copies of the G908R variant significantly increase Crohn's disease risk

The CC genotype means both copies of your NOD2 gene carry the G908R mutation, resulting in severely compromised bacterial sensing capability throughout your intestinal epithelium. This has cascading effects: Paneth cells in your small intestine produce reduced levels of alpha-defensins (antimicrobial peptides), bacterial clearance from intestinal crypts is impaired, and the normal immune response to bacterial peptidoglycan is blunted. Mouse studies show that complete NOD2 deficiency leads to increased bacterial loads in the terminal ileum and greater susceptibility to pathogenic bacterial colonization. In humans, this translates to altered microbiome composition—even in healthy carriers—with increased abundance of certain bacterial families like Erysipelotrichaceae. The variant affects primarily ileal (small intestine) rather than colonic Crohn's disease, reflecting the high expression of NOD2 in ileal Paneth cells.