- Last Update On : 2013-03-09
The Sm and nuclear ribonucleoprotein (RNP) antigens are a particulate complex composed of small nuclear RNAs (U-RNAs) and proteins. This complex has also been referred to as extractable nuclear antigens (ENA), since it is soluble in saline. Autoantibodies to these antigens occur in systemic lupus erythematosis and mixed connective tissue disease.
The Sm (Smith) and related nuclear ribonucleoproteins (nRNPs) are targets for autoantibodies in SLE. These antigens are present in subcellular organelles called spliceosomes that are composed of peptide containing small RNAs. Anti-Sm antibodies are only present in 15 to 30% of the patients with SLE, but they are highly specific for SLE. They occur more frequently (60%) in young black females with SLE. They almost never occur in healthy individuals or patients with other diseases. Anti-Sm antibodies should not be confused with anti-smooth muscle antibodies detected in autoimmune liver disease. Anti-RNP antibodies, which are commonly