Synonyms: Extractable nuclear antigens, antibodies to
Clinical significance
ENA (extractable nuclear antigens) are protein antigens extracted from the cell nucleus. In autoimmune diseases, various types of antibodies are produced against these nuclear proteins, which are no longer recognised as “self” (loss of immune tolerance). The most commonly found anti-ENA antibodies are anti-Sm, SSA/Ro, SSB/La, RNP, Scl-70 and Jo-1. The autoimmune diseases they are associated with include systemic lupus erythematosus (SLE), systemic sclerosis, dermatomyositis, Sjögren’s syndrome (sicca syndrome) and mixed connective tissue disease.
Clinical indications
Systemic autoimmune diseases (SLE, scleroderma, dermatomyositis, Sjögren’s syndrome, mixed connective tissue disease).
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
Notes
Anti-Sm antibodies are specific for SLE, but are found in only 25% of cases. Anti-RNP antibodies, less specific than anti-Sm, are found in 40% of cases of SLE and in mixed connective tissue disease. Anti-SSA/Ro is common in Sjögren’s syndrome (40%); it can also be found in some rare so-called “seronegative” cases of SLE in which ANA are absent. Anti-SSB/La is present in 15% of cases of Sjögren’s syndrome and in SLE. Anti-Scl-70 is found in 80% of cases of progressive systemic sclerosis, and less often (up to 10%) in CREST syndrome. Anti-Jo-1 is characteristic of polymyositis and dermatomyositis.