Description
Anti-Smith antibodies are present in some cases of systemic lupus erythematosus (SLE) and mixed connective-tissue disease (MCTD). Smith antigens are part of the extractable nuclear antigens (ENAs); specifically, they are the proteins that are resistant to ribonuclease. Ribonucleoproteins, the other part of ENAs, are ribonuclease susceptible. [5]
Smith antigens, along with RNP antigens, are part of small nuclear RNAs. Levels of antibodies to these two antigens are often elevated in SLE. The Smith antigen is composed of the B1, D, and E proteins. [4]
Research indicates that anti-Smith antibodies are also more common in persons with cutaneous lupus erythematosus (CLE) who progress to SLE than in CLE patients who do not. These antibodies have also been found more often when subacute CLE or chronic CLE is diagnosed concomitantly with SLE. [6]
Indications/Applications
Anti-Smith antibody testing should be considered in patients with signs or symptoms of SLE or MCTD, such as the following:
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Malar rash
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Discoid rash
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Photosensitivity
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Mucosal ulcers
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Avascular necrosis
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Anemia
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Arthritis/arthralgia
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Serositis
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Glomerulonephritis
