TNF-alpha is a cytokine known to cause inflammation and related symptoms in several chronic inflammatory diseases, such as rheumatoid arthritis (RA), ankylosing spondylitis (SpA), psoriatic arthritis (PsA), plaque psoriasis, Crohn’s disease (CD), and ulcerative colitis (UC) (European Medicines Agency, 2014; European Medicines Agency, 2019d; European Medicines Agency, 2020b). The gene discussed is TNF; the disease is psoriatic arthritis.