Clinical Relevance of Measurement of Antibodies to Individual snU1-RNP Proteins, Ariane Luyckx,1 René

uz.kuleuven.ac.be) Anti-ribonucleoprotein (RNP) antibodies are found in mixed connective tissue disease (MCTD), a syndrome characterized by features of systemic lupus erythemato-sus (SLE), inflammatory muscle disease, and scleroderma (1). High titers of anti-RNP antibodies support the diag-nosis of MCTD, and testing should be ordered when the diagnosis is suspected (2). Anti-RNP antibodies are also found in rheumatic diseases such as SLE, Sjögren syn-drome, rheumatoid arthritis, polymyositis, and systemic sclerosis (2). The antigens to which anti-RNP antibodies react reside in many proteins (70 kD, protein A, and protein C) complexed with small nuclear U1-RNA. This complex is called small nuclear U1 ribonucleoprotein (snU1-RNP)