Genotyping studies have shown that the IL-33 rs10975519 CC genotype in females is associated with a decreased risk of developing rheumatoid arthritis [168], while the IL-33 rs16924159 AA genotype correlates with higher disease activity and poorer clinical outcomes in patients with rheumatoid arthritis and ankylosing spondylitis following treatment with TNF inhibitors; this suggests that IL-33 gene polymorphisms may be potential candidate biomarkers of disease susceptibility and anti-TNF treatment response [168]. Here, TNF is linked to ankylosing spondylitis.