Tocilizumab and Sarilumab are first-line biological disease-modifying anti-rheumatic drug (bDMARD) which inhibits Interleukin 6 (IL-6) pathway through blockade of its receptor on the treatment of Rheumatoid Arthritis and other rheumatic diseases as Giant Cell Arteritis, Still's disease and Idiopathic Juvenile Arthritis. At present, there is a lack of evidence to recommend the treatment of one bDMARD over another. Seeking for genetic biomarkers to predict response to treatment could be key towards a personalized treatment strategy in rheumatology.

The investigators aime to evaluate whether functional single nucleotide polymorphisms (SNPs) in the IL6R gene could predict response and/or toxicity in patients with rheumatic diseases treated with anti-IL-6 receptor drugs.

Inclusion Criteria:

• Diagnosis of Rheumatoid Arthritis by the American College of Rheumatology (ACR) 2010 criteria or
• Diagnosis of Giant Cell Arteritis by the International League of Associations for Rheumatology (ILAR) criteria or
• Diagnosis of Still disease by classification criteria (Yamaguchi et al.) or
• Diagnosis of Idiopathic Juvenile Arthritis by ACR 1990 criteria.
• All of the previous must have been treated with anti-IL-6R monoclonal antibodies in the last 5 years

Exclusion Criteria:

• <18 years at recruitment
• Another rheumatic disease different of the ones in the inclusion criteria

Patients being followed-up in the Hospital de la Santa Creu i Sant Pau, diagnosed of Rheumatoid Arthritis, Idiopathic Juvenile Arthritis, Still disease or Giant Cell Arteritis treated with anti-IL6R drugs.