Genetic studies of anti-Ro (SSA) antibodies in families with rheumatoid arthritis.

Forty-nine members of 4 families with multiple cases of rheumatoid arthritis (RA) were investigated. Nine patients with RA, one patient with primary Sjögren's syndrome (SS) and one patient with systemic lupus erythematosus (SLE) were detected among them. Anti-Ro (SSA) antibodies were found in 11 members (22%) of the investigated group; 6 suffered from RA, SLE or primary SS, and 5 were healthy first degree relatives. Anti-La (SSB) antibodies were detected in only one family member with primary SS. Secondary SS was evident in 5 patients with RA, 3 of whom had anti-Ro antibodies; HLA-DR4 was present in 7 of 9 patients with RA (78%) but in only 7 of 26 asymptomatic relatives (27%) (p less than 0.05). All patients with RA and their relatives who had anti-Ro antibodies were found to have HLA-DR4. Our results demonstrate that anti-Ro antibodies are present in relatives of patients with RA and are strongly associated with HLA-DR4.