Abstract
HLA phenotypes were determined in 50 patients with psoriasis alone and in 50 patients with psoriasis and psoriatic arthritis. Positive associations were found in both groups with B13, B17, B37, Cw6, and DR7, and in addition with C4A6. Higher relative risks were found in respect to the patients with psoriasis alone compared with those with arthritis, and this suggests the involvement of additional genetic factors predisposing to peripheral arthritis. In patients with psoriasis only, the presence of Cw6 was associated with a significantly earlier age of onset.