Table 1.

Characteristics of the study subjects^*

	Controls (n = 56)	Patients with persistent oligoarticular JIA (n = 39)	Patients with RF-negative polyarticular JIA (n = 45)	Patients with systemic JIA (n = 20)
No. with early/late disease onset	–†	23/16	18/27	14/6
Age at onset, mean ± SD years	NA	5.9 ± 4.2	7.4 ± 4.7	5.3 ± 4.7
Disease duration at sampling, mean ± SD years	NA	0.4 ± 0.3	0.7 ± 0.6	0.3 ± 0.5
Age at sampling, mean ± SD years	9.1 ± 5.1	6.3 ± 4.3	8.1 ± 4.7	5.6 ± 4.6
Female sex, %	57	69	87	35
ANA positive, no./no. tested	ND	16/37	17/34	2/5

^*JIA = juvenile idiopathic arthritis; RF = rheumatoid factor; NA = not applicable; ANA = antinuclear antibody; ND = not determined.

^†In the case of controls, their age at the time of sampling was used (20 were age <6 years and 36 were age ≥6 years).