Biomarkers Identification of Anti-tumor Necrosis Factor (TNF) α Agent's Efficacy in Ankylosing Spondylitis Patients

Inclusion Criteria: * AS according to Portuguese Society of Rheumatology (SPR) guidelines (1984 modified New York Criteria, but allowing the use of MRI as imagiological criteria) * Patient enrolment followed national guidelines for TNF antagonist use for the treatment of AS * Adults between 18 to 75 years * Ability to provide informed consent * Corticosteroid therapy allowed (equivalent to ≤ 10 mg prednisone) and / or NSAID(nonsteroidal antiinflammatory drug), stable dose in 4 weeks before study initiation * Adequate contraception (barrier or hormonal) in men and women of childbearing age (patients and their partners * Adequate renal and hepatic function (2 times ULN) Exclusion Criteria: * Current pregnancy or breastfeeding * Previous treatment with biologic DMARD's (disease-modifying antirheumatic drug) * Intraarticular injections or infiltrations of extraaxial joints and tendons within 28 days before or at screening, or intraarticular injections of sacroiliac joints ≤ 28 days before screening * History of rheumatic disorder other than AS * Other forms of spondylarthritis than AS * Any uncontrolled medical condition (e.g., uncontrolled diabetes mellitus, unstable ischemic heart disease) * History or signs of demyelinating disease * Malignancy (except for completely treated squamous or basal cell carcinoma) * Moderate to severe heart failure (NYHA class III/IV) Positive serology for hepatitis B, hepatitis C, or human immunodeficiency virus * Active or latent tuberculosis (TB) or histoplasmosis or other severe infections such as sepsis, and opportunistic infections * Infections requiring hospitalization or intravenous treatment with antibiotics within 30 days or oral treatment with antibiotics within 14 days before enrollment * Ankylosis of the spine (syndesmophytes presence at all levels from D12 to S1 in X-ray (XR) lateral view) * Hypersensitivity to the active substance or to any of the excipients