The most studied TNF-α SNP is located at −308 position, where the presence of rare A allele was associated with a major gene expression, high level of TNF-α expression, and more aggressive JIA phenotypes [36, 43, 74] such as systemic juvenile arthritis and rheumatoid factor positive juvenile polyarticular arthritis [13, 74]. The gene discussed is TNF; the disease is polyarticular juvenile idiopathic arthritis.