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Background and Aims: Register-based research suggests a shared pathophysiology between inflammatory bowel disease IBD and spondyloarthritis SpA, but the role of familial genetic and environmental factors in this shared susceptibility is largely unknown. We aimed to compare the risk of SpA in first-degree relatives FDRs and spouses of IBD patients with FDRs and spouses of matched, population-based, reference individuals. Methods: We identified 147 080 FDRs and 25 945 spouses of patients with incident IBD N = 39 203 during 2006-2016, and 1 453 429 FDRs and 258 098 spouses of matched reference individuals N = 390 490, by linking nationwide Swedish registers and gastrointestinal biopsy data. Study participants were followed 1987-2017. Cox regression was used to estimate hazard ratios HRs of SpA. Results: During follow-up, 2430 FDRs of IBD patients 6.5/10 000 person-years and 17 761 FDRs of reference individuals 4.8/10 000 person-years were diagnosed with SpA, corresponding to an HR of 1.35 95% CI:1.29, 1.41. In subgroup analyses, the increased risk of SpA was most pronounced in FDRs of Crohn's disease patients HR = 1.44; 95% CI:1.34,1.5 6 and of IBD patients aged <18 years at diagnosis HR = 1.46; 95% CI: 1.27, 1.68. IBD patients' spouses also had a higher SpA rate than reference individuals' spouses, but the difference was less pronounced 4.3 vs 3.5/10 000 person-years; HR = 1.22; 95% CI:1.09, 1.37. No subgroup-specific risk pattern was identified among spouses. Conclusions: The observed shared familial risks between IBD and SpA support shared genetic factors in their pathogenesis. However, spouses of IBD patients were also at increased risk for SpA, reflecting the influence of environmental exposures or similarities in health-seeking patterns.
Shrestha et al. (2024) studied this question.