Genome-wide association analysis of diverticular disease points towards neuromuscular, connective tissue and epithelial pathomechanisms

OBJECTIVE

Diverticular disease is a common complex disorder characterised by mucosal outpouchings of the colonic wall that manifests through complications such as diverticulitis, perforation and bleeding. We report the to date largest genome-wide association study (GWAS) to identify genetic risk factors for diverticular disease.

DESIGN

Discovery GWAS analysis was performed on UK Biobank imputed genotypes using 31 964 cases and 419 135 controls of European descent. Associations were replicated in a European sample of 3893 cases and 2829 diverticula-free controls and evaluated for risk contribution to diverticulitis and uncomplicated diverticulosis. Transcripts at top 20 replicating loci were analysed by real-time quatitative PCR in preparations of the mucosal, submucosal and muscular layer of colon. The localisation of expressed protein at selected loci was investigated by immunohistochemistry.

RESULTS

We discovered 48 risk loci, of which 12 are novel, with genome-wide significance and consistent OR in the replication sample. Nominal replication (p<0.05) was observed for 27 loci, and additional 8 in meta-analysis with a population-based cohort. The most significant novel risk variant rs9960286 is located near CTAGE1 with a p value of 2.3×10^-10 and 0.002 (OR_allelic=1.14 (95% CI 1.05 to 1.24)) in the replication analysis. Four loci showed stronger effects for diverticulitis, PHGR1 (OR 1.32, 95% CI 1.12 to 1.56), FAM155A-2 (OR 1.21, 95% CI 1.04 to 1.42), CALCB (OR 1.17, 95% CI 1.03 to 1.33) and S100A10 (OR 1.17, 95% CI 1.03 to 1.33).

CONCLUSION

In silico analyses point to diverticulosis primarily as a disorder of intestinal neuromuscular function and of impaired connective fibre support, while an additional diverticulitis risk might be conferred by epithelial dysfunction.

[How should patients with completely resected gastrointestinal stromal tumours (GIST) be followed up?]

Gastrointestinal stromal tumours are topical because of their uncertain biological behaviour and the potential of treatment with imatinib. In the following study we have examined which pattern of follow-up is both appropriate for detecting recurrences and cost-effective.

PATIENTS AND METHODS

Between July 1997 and February 2004 we treated 43 patients diagnosed with a GIST. Patients with high risk (HR), intermediate risk (IR), or overtly malignant (OM) tumours were followed-up regularly. In 2004 we screened all patients independent of their risk of malignant disease with an ultrasound scan and endoscopy followed by endosonography. Further diagnostic procedures were carried out if necessary.

RESULTS

Overall, we diagnosed recurrences in five out of 33 patients at risk (two in patients with OM, one in a patient with HR, and 2 in patients with IR according to the NIH criteria). The time period between resection of the primary tumour and recurrence ranged from 4.5 to 33 months. One of the patients with a recurrence was seen before the imatinib era, the other four were treated with imatinib mesylate.

CONCLUSION

In our experience, regular follow-up should be restricted to patients with OM, HR, and IR GIST. We suggest that patients are initially seen in six months intervals for two years and annually for another three years thereafter.