To characterize juvenile idiopathic arthritis (JIA) patients from multicase families.
The study series comprised 80 affected siblings belonging to 37 families. Comparisons were made with a population-based series of JIA patients from Finland and with a sibling series from the United States.
The distribution of cases according to onset type was similar in the sibling and population-based series. The age at diagnosis was significantly lower in the sibling series (4.8 years vs 7.4 years; p < 0.001). There was more intra-pair similarity in onset and course types in the United States series compared to the Finnish series and the proportion of girls was higher in the former.
The only significant difference between familial and sporadic cases with JIA is an earlier onset of disease in familial cases. There is no essential difference in clinical features of the disease between patients in the multicase and sporadic groups. Differences between the Finnish and US series may be due to selection bias in the latter.