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Eijsbouts C, Zheng T, Kennedy NA, et al. Genome-wide analysis of 53,400 people with irritable bowel syndrome highlights shared genetic pathways with mood and anxiety disorders. Nat Genet. 2021;53(11):1543-1552. PMID 34741163

One-paragraph summary

The investigators designed a digestive health questionnaire for UK Biobank, combined the identified IBS cases with independent cohorts (the Bellygenes Initiative and others), and conducted a genome-wide association study of 53,400 cases and 433,201 controls, replicating significant associations in a 23andMe panel of 205,252 cases and 1,384,055 controls. Six genetic susceptibility loci for IBS were identified and confirmed, implicating NCAM1, CADM2, PHF2/FAM120A, DOCK9, CKAP2/TPTE2P3 and BAG6. The first four are associated with mood and anxiety disorders, are expressed in the nervous system, or both. Genome-wide genetic correlation between IBS and anxiety, neuroticism and depression exceeded rg > 0.5. Additional analyses indicated that this correlation arises from shared pathogenic pathways rather than, for example, anxiety causing abdominal symptoms.

Key findings

  • Six replicated susceptibility loci — the first robust common-variant findings in IBS at scale.
  • Implicated genes are predominantly nervous-system genes, not gut-epithelial or immune genes.
  • Genetic correlation with anxiety, neuroticism and depression rg > 0.5, among the highest reported between a gastrointestinal condition and psychiatric traits.
  • The shared-pathway interpretation directly contradicts the simple psychosomatic reading in which psychological distress causes bowel symptoms.
  • Effect sizes at individual loci are small; no polygenic score is clinically usable.

Limitations

  • Case definition rests on questionnaire-derived and self-reported IBS across heterogeneous cohorts, not on uniformly applied Rome criteria — the criteria-dependence problem that pervades this field applies here too.
  • Predominantly European-ancestry samples; portability to other ancestries is untested.
  • Six loci explain a small fraction of heritability; the architecture is highly polygenic and mostly uncharacterised.
  • Directionality inference (shared pathways rather than anxiety→symptoms) rests on statistical genetic methods with their own assumptions, not on experiment.
  • 23andMe replication cases are consumer-reported.

Why it matters

This is the study that made IBS genetically tractable, and its central result reframes the condition's most persistent controversy. For decades the co-occurrence of IBS with anxiety and depression was read either as psychological causation or as the psychological consequence of chronic symptoms; longitudinal cohorts had already shown the relationship runs both ways (Koloski 2012, PMID 22234979). Eijsbouts adds a third reading with genetic evidence behind it: the two share pathogenic pathways. That has direct clinical consequences — it is the strongest argument that gut–brain neuromodulators are acting on a shared substrate rather than treating comorbid depression, consistent with ATLANTIS finding symptom benefit with no change in anxiety or depression scores (Wright-Hughes 2024, PMID 39397570). It also sets the agenda for the field's biggest unsolved problem: none of the six loci has yet produced a biomarker or a drug target.

Cited by wiki pages

  • brain-gut-axis-and-visceral-hypersensitivity
  • post-infectious-ibs
  • gut-brain-neuromodulators
  • overview