Familial Aggregation of Childhood- and Adulthood-Onset Systemic Lupus Erythematosus.

Objective: To assess the familial occurrence of systemic lupus erythematosus (SLE) in a large Brazilian cohort.

Methods: Consecutive patients with SLE were recruited and stratified according to age at disease onset into childhood-onset SLE or adult-onset SLE. Each patient was personally interviewed regarding the history of SLE across 3 generations (first-, second-, and third-degree relatives). Recurrence rates were analyzed for each degree of relation.

Results: We included 392 patients with SLE (112 with childhood-onset SLE and 280 with adult-onset SLE). We identified 2,574 first-degree relatives, 5,490 second-degree relatives, and 6,805 third-degree relatives. In the combined overall SLE cohort, we observed a familial SLE recurrence rate of 19.4 in first-degree relatives, 5.4 in second-degree relatives, and 3.0 in third-degree relatives. Recurrence rates were higher for first- and second-degree relatives of patients with childhood-onset SLE than for first- and second-degree relatives of patients with adult-onset SLE (25.2 versus 18.4 for first-degree, and 8.5 versus 4.5 for second-degree), while in third-degree relatives, recurrence rates were higher in adult-onset SLE than in childhood-onset SLE (P = 2.2 × 10 for differences in recurrence proportions between childhood-onset SLE and adult-onset SLE). There were no phenotypic differences in patients from multicase versus single-case families, and there was no sex-skewing observed in the offspring of patients with SLE.

Conclusion: The greater decline in SLE recurrence rate by generation in childhood-onset SLE versus adult-onset SLE suggests a more polygenic and epistatic inheritance and suggests that adult-onset SLE may be characterized by fewer risk factors that are individually stronger. This finding suggests a higher genetic load in childhood-onset SLE versus adult-onset SLE and a difference in the genetic architecture of the disease based on age at onset.