rs2241880 — ATG16L1 T300A

Autophagy gene variant affecting bacterial clearance in gut epithelial cells, strongly associated with Crohn's disease risk

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ATG16L1 T300A — Autophagy, Gut Health, and Crohn's Disease Risk

The ATG16L1 gene provides instructions for making a protein essential to autophagy, the cellular recycling system that clears out damaged components and invading bacteria. The T300A variant11 The T300A variant
This threonine-to-alanine substitution at position 300 is one of the most replicated genetic risk factors for Crohn's disease, first identified in a genome-wide association study in 2007 and subsequently confirmed in dozens of independent cohorts worldwide. In the gut, ATG16L1 plays a critical role in Paneth cells, specialized epithelial cells that secrete antimicrobial peptides and maintain the intestinal barrier. The T300A variant impairs this function, allowing bacteria to persist when they would normally be destroyed.

The Mechanism

The T300A variant sits near a caspase-3 cleavage site22 The T300A variant sits near a caspase-3 cleavage site
Amino acids 296-299 form a caspase cleavage motif, and the T300A substitution significantly increases the protein's susceptibility to caspase-3-mediated degradation during cellular stress. When cells experience metabolic stress, death receptor activation, or starvation, caspase-3 degrades the T300A variant more rapidly than wild-type ATG16L1, resulting in diminished autophagy. This leaves epithelial cells less able to clear invading bacteria like Salmonella and Yersinia enterocolitica. Studies in human epithelial cells show the T300A variant has markedly decreased efficiency33 the T300A variant has markedly decreased efficiency
The ala300-containing variant showed decreased capture of internalized Salmonella within autophagosomes compared to the wildtype thr300-containing variant in capturing bacteria within autophagosomes. The variant also disrupts the WD40 domain's ability to interact with proteins like TMEM59, further impairing unconventional autophagy pathways.

The Evidence

Multiple meta-analyses confirm the T300A association with Crohn's disease44 Multiple meta-analyses confirm the T300A association with Crohn's disease
Meta-analysis of 30,606 IBD patients found the G allele was a risk factor (OR 1.23, 95% CI: 1.09-1.39, p=0.001) while the A allele was protective (OR 0.74, 95% CI: 0.72-0.77, p<0.001). The association is strongest in Caucasian populations from North America, Europe, and Latin America, with minimal to no association observed in Asian populations. CD patients carrying the G allele are significantly more predisposed to perianal disease55 CD patients carrying the G allele are significantly more predisposed to perianal disease
OR 1.21, 95% CI: 1.07-1.38, p=0.003, one of the more severe and treatment-resistant manifestations of Crohn's. A 2025 meta-analysis found the G allele increases CD risk worldwide66 A 2025 meta-analysis found the G allele increases CD risk worldwide
OR 1.33, 95% CI: 1.29-1.37, with GG homozygotes showing higher risk than AG heterozygotes. The variant also alters gut microbiota composition—studies in knock-in mice show increased Bacteroides ovatus and elevated Th17 and Th1 immune cells77 studies in knock-in mice show increased Bacteroides ovatus and elevated Th17 and Th1 immune cells
Changes occur before disease onset, suggesting T300A contributes to dysbiosis and immune infiltration prior to symptoms.

Practical Implications

This variant doesn't cause Crohn's disease on its own—it's a susceptibility factor that increases risk in the presence of environmental triggers like smoking, certain infections, or dietary patterns that stress the gut. For those with the GG genotype (about 19% of Europeans), maintaining gut barrier integrity becomes especially important. This means prioritizing dietary fiber, fermented foods, and avoiding pro-inflammatory processed foods and excessive antibiotic use. Regular monitoring for early signs of inflammatory bowel disease (persistent diarrhea, abdominal pain, blood in stool) allows for earlier intervention. The variant's impact on bacterial clearance also suggests that individuals with GG may benefit from strategies that support innate immunity and gut microbial diversity.

Interactions

ATG16L1 T300A interacts with other Crohn's disease susceptibility genes through multiple pathways. Multidimensionality reduction analysis shows interaction between ATG16L1, IBD5 (rs6596075), and IL23R (rs10889677) risk alleles88 Multidimensionality reduction analysis shows interaction between ATG16L1, IBD5 (rs6596075), and IL23R (rs10889677) risk alleles
MDR analysis suggested an interaction between IBD5, ATG16L1, and IL23R risk alleles, with combined carriage of multiple risk variants substantially increasing CD risk. NOD2 (rs17221417) is particularly important— NOD2 recruits ATG16L1 to sites of bacterial entry99 NOD2 recruits ATG16L1 to sites of bacterial entry, so NOD2 mutations combined with ATG16L1 T300A produce a synergistic defect in bacterial autophagy. Individuals homozygous for risk alleles at ATG16L1, IBD5, and NOD2 face approximately 20-fold higher CD risk1010 Individuals homozygous for risk alleles at ATG16L1, IBD5, and NOD2 face approximately 20-fold higher CD risk
OR 20.4, CI 8.71-47.7 compared to those carrying none of these variants. IL23R variants also show statistical interaction, as IL23R regulates the Th17 immune response that becomes dysregulated when ATG16L1-mediated bacterial clearance fails.

Nutrient Interactions

probiotics altered_metabolism
fiber altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

AA Normal Autophagy Normal

Standard gut epithelial barrier function and bacterial clearance

You have two copies of the protective A allele (threonine at position 300), encoding the standard form of ATG16L1 that maintains normal autophagy function. Your gut epithelial cells can efficiently capture and destroy invading bacteria, and your Paneth cells produce appropriate levels of antimicrobial peptides. About 32% of people of European descent share this genotype. This is the ancestral, wild-type form that has not been associated with increased inflammatory bowel disease risk.

AG Intermediate Autophagy Intermediate

Moderately increased Crohn's disease susceptibility, one copy of the risk variant

You have one copy of the G risk allele (alanine at position 300) and one protective A allele. This intermediate genotype is carried by about 49% of people of European descent and confers moderately increased risk for Crohn's disease (OR approximately 1.3). Your ATG16L1 protein has reduced stability under cellular stress, leading to somewhat impaired bacterial clearance in gut epithelial cells. The effect is dose-dependent—one copy produces a milder impact than two copies.

GG Impaired Autophagy Reduced

Significantly increased Crohn's disease risk, reduced bacterial clearance in gut cells

You have two copies of the G risk allele, encoding the alanine-300 variant that is highly susceptible to caspase-3 degradation during cellular stress. About 19% of people of European descent carry this genotype, which is associated with approximately 1.7-1.9 fold increased risk for Crohn's disease and increased risk for perianal disease. Your gut epithelial cells show markedly reduced efficiency in capturing and destroying invading bacteria, and your Paneth cells may produce dysregulated antimicrobial peptides. This doesn't mean you will develop Crohn's disease—most GG carriers never do—but environmental triggers (infections, smoking, diet, stress) carry higher stakes for your gut health.