Objective: To describe the demographics and clinical disease in affected sibpairs (ASPs) with juvenile rheumatoid arthritis (JRA), and to compare JRA as it occurs in ASPs with that from non-ASP JRA populations described in the literature.
Methods: A rare disease research registry was established with a focus on JRA ASPs to facilitate accrual of patients for genetic, epidemiologic, and clinical studies. Physicians likely to care for patients with JRA were made aware of the registry and its goals by a variety of methods and asked to refer patients for entry.
Results: To date, 71 ASPs have been registered and complete information has been obtained. These affected sibs differed in age by a mean of 4.1 years (SD 3.4) and in age at disease onset by 2.8 years (SD 3.0). The actual time difference between onset in sib 1 versus sib 2 averaged 4.4 years (SD 4.2). Sixty-three percent of the sibpairs were concordant for sex, and 76% for JRA onset type. Onset type within sibpairs did not appear to be random, based upon comparisons with non-ASP populations. Greater than expected concordance was seen among those with pauciarticular-onset and polyarticular-onset JRA. Seventy-nine percent of the pairs were concordant for course type. Seven sets of twins were included (approximately 10% of the total), all were concordant for onset and course type (6 sets with pauciarticular, 1 set with polyarticular), and disease onset was separated by a mean of only 3.3 months. Within the onset and course types, the clinical disease, such as the female:male ratio, age at onset, and serologic findings, in ASPs resembled that which has been described in the literature.
Conclusion: A higher than expected degree of concordance for onset type of JRA exists between sibpairs, indicating that genetic influences play a role. Affected sibs do not tend to develop their disease at approximately the same point in time, except for the twin sets. Clinical features of the disease within the various subtypes appear similar to those in non-ASP populations.