Do IL23R and MST1 genetic variants increase IBD risk and contribute to iron and vitamin D insufficiency?

Genetic variations in IL23R and MST1 are well-established risk factors for Inflammatory Bowel Disease (IBD), influencing the condition through distinct immunological and structural pathways that can ultimately impact systemic nutrient status.

Clinical evidence of IBD risk

Extensive genomic studies confirm that specific polymorphisms in these genes significantly modulate IBD susceptibility.

• IL23R variation: The IL23R rs11209026 (Arg381Gln) variant is a highly replicated protective marker. The minor A allele (Gln381) reduces the risk of Crohn’s disease by approximately 62% (OR ~0.38) and Ulcerative Colitis by about 27% (OR ~0.73).
• MST1 variation: Conversely, the MST1 rs3197999 (R689C) polymorphism is a risk-increasing variant (p = 3.62 × 10⁻⁶) consistently identified across diverse IBD populations.

Mechanistic pathways and barrier dysfunction

These genetic variations influence the gut barrier through the regulation of inflammation and epithelial repair.

• Immune signaling: The protective IL23R variant functions as a loss-of-function allele, dampening the Th17 inflammatory response by reducing STAT3/STAT4 phosphorylation. This reduces chronic immune-mediated damage to the intestinal lining.
• Epithelial homeostasis: MST1 (STK4) is a core component of the Hippo signaling pathway, which is essential for regulating intestinal epithelial cell proliferation and architectural integrity. Loss of MST1 function leads to uncontrolled stem cell proliferation and disrupted barrier turnover.
• Mucosal repair: IL23R signaling in epithelial cells is necessary for the induction of IL-22, a cytokine critical for antimicrobial peptide production (e.g., Reg3b) and rapid mucosal healing following injury.

Impact on nutrient absorption

A compromised intestinal barrier directly interferes with the absorption of critical micronutrients through inflammatory interference and structural damage.

• Iron insufficiency: Inflammation-driven barrier dysfunction triggers the upregulation of hepcidin and the downregulation of duodenal iron transporters. Chronic "leaky gut" states can further exacerbate iron loss through microscopic fecal bleeding.
• Vitamin D deficiency: As a fat-soluble nutrient, Vitamin D absorption is hindered by bile acid dysregulation and dysbiosis, both frequent consequences of impaired barrier integrity. Clinical data show that patients with active IBD and high markers of permeability (e.g., fecal zonulin) have significantly lower serum iron and Vitamin D3 levels compared to those in remission.

Bottom line

Genetic variations in IL23R and MST1 are robustly linked to IBD risk. These variants contribute to gut barrier dysfunction by impairing mucosal repair and promoting chronic inflammation, which subsequently disrupts the transport mechanisms required for maintaining adequate iron and vitamin D levels.