The authors describe the clinical pictures of different types of juvenile arthritis, which are divided according to the newly recommended classification of ILAR (International League of Associations for Rheumatology). Thus seven homogeneous groups are obtained into which the children are included after a 6-month persistence of the disease. Each group is clearly defined according to classification criteria. It is assumed that in the pathogenesis of different types of juvenile arthritis different genetic factors participate. Most is known about the association with HLA genes, but the participation of other genes is also probable, e.g. genes which code for pro-inflammatory cytokines and their inhibitors. In the authors’ patients a significantly higher ratio of allele 2 of the gene for the interleukin 1 receptor antagonist (IL-1Ra) was found.

        Key words: juvenile idiopathic arthritis