The coexistence of rheumatoid arthritis with Reiter's syndrome and/or ankylosing spondylitis: a model of dual HLA-associated disease susceptibility and expression.

In a prospective study of 184 patients with ankylosing spondylitis and/or Reiter's disease, we have examined the frequency of concomitant rheumatoid arthritis (RA) and determined the HLA profile of these patients. Five men (2.7%), 3 with ankylosing spondylitis and 2 with Reiter's disease, had coexistent classical RA and 2 of these also had Felty's syndrome. Immunogenetic analysis demonstrated that all 5 patients had either HLA-R27 or another B-7-cross-reactive antigen and that 3 also possessed HLA-DR4. Thus, 2 or more HLA-associated genetic predispositions may occur in the same individual, and, when expressed, result in the dual expression of both a spondylitic disease and RA.