At the same time, TNFα has a powerful proinflammatory effect [11], but in the present work it was shown that the TNFA rs1800629*A allele in the TNFA rs1800629*A - LTA rs909253*G haplotype acts as a protective marker in relation to the insufficient response to methotrexate in girls with JIA. The gene discussed is TNF; the disease is juvenile idiopathic arthritis.