rs104895444 — NOD2

NOD2 Val793Met — A Rare Variant in the Gateway to Gut Immunity

The NOD2 gene encodes a cytosolic pattern recognition receptor¹¹ pattern recognition receptor
NOD2 senses muramyl dipeptide (MDP), a fragment of bacterial cell-wall peptidoglycan that detects bacterial cell-wall fragments and mounts an immune defense in the intestinal lining. It was the first gene identified for Crohn's disease²² the first gene identified for Crohn's disease
NOD2 was discovered as a susceptibility locus in the IBD1 linkage region on chromosome 16q12 susceptibility and remains the most studied single gene in inflammatory bowel disease genetics. The rs104895444 variant changes valine to methionine at protein position 793 (Val793Met), a site within the leucine-rich repeat domain that participates in bacterial ligand sensing.

The Mechanism

NOD2 protein consists of two N-terminal CARD (caspase-recruitment) domains³³ CARD (caspase-recruitment) domains
CARDs mediate protein-protein interactions that activate the NF-κB signaling cascade, a central NOD domain, and C-terminal leucine-rich repeats (LRRs). The LRR domain directly recognizes muramyl dipeptide (MDP), the minimal bioactive peptidoglycan fragment from both Gram-positive and Gram-negative bacteria. Successful MDP binding triggers NOD2 oligomerization, RIPK2 recruitment, and downstream NF-κB activation⁴⁴ NF-κB activation
NF-κB activates genes encoding antimicrobial peptides (defensins), pro-inflammatory cytokines, and barrier-strengthening proteins — a coordinated response that clears bacteria while reinforcing the epithelial barrier.

The Val793Met change lies within the LRR domain at a position conserved across mammals. While ClinVar currently classifies this variant as likely benign based on existing submissions, it was identified in deep resequencing⁵⁵ identified in deep resequencing
Rivas et al. 2011 whole-exome resequencing of 16,054 CD and 12,153 UC cases identified V793M among additional rare NOD2 risk variants beyond the three classic mutations as one of several rare NOD2 missense variants independently associated with IBD in a genome-wide study of over 45,000 individuals. The substitution of valine (a small non-polar amino acid) for methionine (a larger sulfur-containing amino acid) could alter LRR domain folding or MDP-binding geometry, potentially reducing the sensitivity of bacterial sensing.

The Evidence

The genetic case for Val793Met rests on its identification in a landmark deep-resequencing study⁶⁶ landmark deep-resequencing study
Rivas et al. sequenced 163 genes in 9 GWAS loci in 16,054 CD cases, 12,153 UC cases, and 17,575 controls, identifying V793M among four additional independent NOD2 risk factors that interrogated over 45,000 IBD cases and controls. The study identified Val793Met (V793M) as one of four additional independent NOD2 risk factors beyond the three classic variants (R702W, G908R, L1007fs), each of which carries odds ratios of 2–4 for heterozygotes and 17–40 for compound heterozygotes or homozygotes.

The broader NOD2-Crohn's connection is established beyond any doubt⁷⁷ established beyond any doubt
More than 145 published studies confirm NOD2 as the strongest non-HLA locus for Crohn's disease. The three classic variants together account for ~80% of NOD2-attributable CD risk in European populations; 27 rare mutations account for the remaining ~20%⁸⁸ 27 rare mutations account for the remaining ~20%
Lesage et al. 2002 found that in 612 IBD patients, the three major variants contributed 81% of disease-associated alleles while 27 rare variants contributed 19%. Val793Met occupies this second tier — rare individually, but clinically meaningful in the context of compound heterozygosity.

The evidence for Val793Met as a standalone risk factor is moderate rather than established: it is supported by one large resequencing study but lacks the replication depth of the three major NOD2 variants. Its individual contribution to Crohn's disease risk is likely modest. The variant's significance is amplified when a second NOD2 hit is present on the opposite chromosome.

Practical Implications

Carriers of one copy of the A allele face a mildly elevated risk for Crohn's disease, primarily through two mechanisms: direct LRR domain disruption and, more importantly, the possibility of compound heterozygosity with another NOD2 variant. Because Val793Met is rare (~0.2% allele frequency in Europeans), most carriers will not have a second NOD2 hit — but those who do face substantially elevated risk.

NOD2-associated Crohn's disease has a characteristic phenotype: ileal or ileocolonic location, fibrostenotic (stricturing) complications, and a tendency toward surgical resection. Patients with two NOD2 mutations⁹⁹ Patients with two NOD2 mutations
Double-dose NOD2 carriers show earlier onset, 53% stricturing rate vs 28%, and more frequent ileal-only disease show earlier disease onset, more stricturing behavior, and higher surgical rates than single-copy carriers or non-carriers.

NOD2 variants are also being used as biomarkers to guide therapy¹⁰¹⁰ biomarkers to guide therapy
NOD2 genotype informs risk of steroid refractoriness, surgical necessity, and consideration of early biologic use decisions in Crohn's disease management. Carriers with established IBD may benefit from early specialist involvement to monitor for fibrostenotic complications.

Interactions

The clinical significance of Val793Met is substantially magnified by compound heterozygosity. When this variant occurs on one chromosome alongside a different NOD2 variant — such as R702W (rs2066844), G908R (rs2066845), or L1007fs (rs2066847) — on the opposite chromosome, both alleles carry impaired function and the net NOD2 activity is severely reduced. Compound heterozygosity for two NOD2 mutations¹¹¹¹ Compound heterozygosity for two NOD2 mutations
In the large NOD2 genotype-phenotype study, double-mutation carriers showed OR ~40 for CD compared to OR ~3-4 for single-copy carriers dramatically amplifies Crohn's disease risk compared to either mutation alone.

The rs104895431 variant in the same batch belongs to the same NOD2 compound heterozygosity risk cluster. Individuals carrying both rs104895444 and rs104895431 on opposite chromosomes would have effectively zero functional NOD2 alleles, creating a high-risk state for Crohn's disease with the ileal-stricturing phenotype typical of double-NOD2-mutation carriers. This interaction is the central clinical significance of both variants — individually rare and modest, combined potentially severe.

NOD2 genotype also interacts with smoking status: NOD2 mutation carriers who smoke¹²¹² NOD2 mutation carriers who smoke
Kuenzig et al. 2017 found NOD2-smoking interaction modified stricturing phenotype risk in CD show modified disease outcomes, with smoking amplifying the stricturing tendency already present with NOD2 variants. The pathobiological pathway converges on the gut microbiome — NOD2-deficient mice develop dysbiosis and intestinal inflammation that mirrors CD, confirming the bacterial-sensing deficit hypothesis¹³¹³ confirming the bacterial-sensing deficit hypothesis
NOD2-knockout mouse models develop altered gut microbiome composition and show heightened intestinal inflammation.