Abstract
OBJECTIVE: To investigate familial aggregation of Sjögren's syndrome (SS) and the relative risks (RRs) of other autoimmune disease in relatives of patients with SS. METHODS: We identified 23,658,577 beneficiaries enrolled in the Taiwan National Health Insurance system in 2010, of whom 12,754 had SS. We identified 21,009,551 parent-child relationships and 17,168,340 pairs of full siblings. The familial risks of SS and other autoimmune diseases, tetrachoric correlation, and familial transmission were estimated. RESULTS: We identified 105 patients with SS who had an affected first-degree relative. The RR of SS was 18.99 (95% confidence interval [95% CI] 9.76-36.93) in siblings of patients with SS, 11.31 (95% CI 8.34-15.33) in offspring, and 12.46 (95% CI 9.34-16.62) in parents. Tetrachoric correlation coefficients were 0.53 (95% CI 0.41-0.65) for cotwins of affected individuals and 0.21 (95% CI 0.16-0.26) for full siblings. The familial transmission (heritability plus shared environmental contribution) was 0.54 (95% CI 0.44-0.77). In first-degree relatives of patients with SS, the RRs were 2.95 (95% CI 2.33-3.73) for rheumatoid arthritis, 6.25 (95% CI 5.15-7.58) for systemic lupus erythematosus, 2.39 (95% CI 0.77-7.41) for systemic sclerosis, 0.71 (95% CI 0.10-5.07) for idiopathic inflammatory myopathy, 1.97 (95% CI 1.29-3.02) for type 1 diabetes mellitus, 3.38 (95% CI 1.26-9.05) for multiple sclerosis, 1.67 (95% CI 0.83-3.33) for myasthenia gravis, 1.25 (95% CI 1.04-1.50) for psoriasis, 1.21 (95% CI 0.39-3.76) for inflammatory bowel disease, and 2.29 (95% CI 1.19-4.40) for vasculitis. CONCLUSION: The risk of SS and other autoimmune diseases is increased in relatives of patients with SS, and more than one-half of phenotypic variance in SS can be explained by familial factors.