Description
Antibodies to the SSA antigen (also known as Ro antigen) are one of the most frequent serological markers of autoimmunity in rheumatic diseases. They appear in 60-70% of patients with Sjögren's syndrome (SS), 30-40% of patients with systemic lupus erythematosus (SLE), and 3-5% of patients with rheumatoid arthritis (RA). The SSA antigen is comprised of an acidic 52 kDa protein that may exist in complex with RNA (80-112 bases). However, RNA is not required for SSA antigenicity. The SSA antigen is predominantly cytoplasmic, and not located in the nucleus. Therefore, patients with antibody to SSA may be ANA negative on routine testing. Approximately 62% of ANA negative lupus patients have antibodies to SSA. Two types of anti-Ro/SSA antibodies have been identified; Ro/SSA antigens of 60 kDa and 52 kDa. Anti-SSA-52 kDa antibodies are linked to certain disorders such as SS, SLE, neonatal lupus and congenital heart block. Clinically, the presence of SSA52 has been reported in a wide variety of diseases, includes inflammatory myositis, primary biliary cirrhosis and SS