[Occurrence of HLA B27 antigen in ankylosing spondylitis in Italy]

39 individuals from Middle and South Italy were selected for being affected by ankylosing spondylitis (AS) (N = 22) or by sacroiliitis (SI) (N = 17) and typed for the HLA system antigens. 320 healthy individuals were typed as control population. The following phenotypic frequencies of HLA-B27 were found; 68% in AS patients, 71% in SI patients and 5% in controls. The frequency of B27 observed among our AS patients is lower than those observed in other caucasian patients. Our data may be explained either by a genetic hypothesis or by an environmental hypothesis; data reported by other authors let we believe that the last one is more reliable.