Compliance with ethical standards: the study was approved by the ethical committee of the S.I. Georgievsky Medical Academy of Vernandsky Crimean Federal University (Federal State Autonomous Educational Institution), minutes protocol #9 of October 14, 2019); it was planned and conducted in accordance with the Declaration of Helsinki, with parents of all JRA patients and healthy children included in the study signing a voluntary informed consent.

Author contribution: AA Elezarov, AS Kucheryavyy — data collection, analysis and interpretation; LN Gumenyuk — research concept and design; LE Sorokina, SR Arifdzhanova, OYu Gerbali — article preparation.