[Familial studies of reactive arthritis].

A survey conducted by the French Society of Rheumatology indicates that 10 p. cent of subjects with reactive arthritis have a family history. This family history can be divided into 3 equal groups of diseases : rheumatic pelvispondylitis, reactive and unclassified arthritis and psoriasis (3.5 p. cent for each condition). The B27 antigen is present in 67 p. cent of cases of reactive arthritis, which is significantly lower than the incidence in rheumatic pelvispondylitis. Informative family studies are presented which demonstrate their value as an in diagnosis, the roles of hereditary factors and the arguments for and against a predisposing gene close to but different from B27.