Background/Purpose:  Genetic factors play a role in SLE, evidenced by the high sibling risk ratio (λs=8–29) and higher concordance rates between monozygotic twins (>35%) compared to dizygotic twins (2-5%). It is clear that the genetic basis of disease differs to some degree between ancestral backgrounds, and is less well understood in non-European ancestry subjects. In this study, we assessed the familial occurrence autoimmune disease in childhood-onset SLE (cSLE) and adult-onset SLE (aSLE) relatives in a large Brazilian cohort.

Methods:  cSLE patients (disease-onset ≤18 years) and aSLE patients (disease-onset >18 years) followed in the Pediatric and Adult Rheumatology Outpatient Clinic of the State University of Campinas were included. Each patient was personally interviewed regarding history of autoimmune diseases in three family generations (grandparents, parents and uncles/aunts, cousins and siblings). Recurrence rates were then calculated for each reported disease.

Results: We included 112 cSLE patients [96 (85.7%) women] and 266 aSLE patients [247 (92.9%) women]. In cSLE patients we identified 3812 relatives. In the first-degree kinship we observed 10 relatives with SLE, with a recurrence rate of 25.3 (25-fold greater risk of SLE than the general population). In the second-degree kinship we observed 10 relatives with SLE and 1193 relatives without, with a recurrence rate of 8.3. In the third-degree kinship we observed a recurrence rate of 0.9 (no increase over general population). In aSLE patients we identified 10584 relatives. In the first-degree kinship we observed a recurrence rate of 18.8. In the second-degree kinship the recurrence rate was4.6. The most frequent non-SLE autoimmune diseases observed in the family members were: hypothyroidism, hyperthyroidism, vitiligo, rheumatoid arthritis, psoriasis, systemic sclerosis, ankylosing spondylitis, inflammatory myopathy, Sjögren syndrome, Crohn’s disease.

Conclusion:  SLE recurrence rate is higher among first-degree relatives in both cSLE and aSLE patients, and steadily decreases between generations as would be expected for complex inheritance. Familial tendency toward SLE was higher in families with a cSLE patient, and recurrence rates were comparable or higher than those reported in European ancestry.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/familial-aggregation-of-autoimmune-diseases-in-childhood-and-adulthood-systemic-lupus-erythematosus/