HLA-B27

A genetic factor (HLA-B27) has been identified that predisposes a person to the disorder. In individuals who carry HLA-B27, symptoms of reactive arthritis may appear suddenly and often are more severe than in persons who are HLA-B27-negative. The condition also tends to affect individuals with weakened immune systems.

…of western European descent are HLA-B27 positive.

…is strongly linked to the HLA-B27 gene variant, which is present in 65 to 96 percent of symptomatic individuals.