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 {{WBRQuestion
|QuestionAuthor=Gerald Chi (Reviewed by  {{YD}})
|ExamType=USMLE Step 1
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathophysiology
|MainCategory=Biochemistry, Pathophysiology
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathophysiology
|MainCategory=Biochemistry, Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|Prompt=A 30-year-old woman presents with mild fever, malaise, and swollen hand and knee joints. Physical examination is remarkable for malar rash. Laboratory findings include lymphopenia with mild anemia and thrombocytopenia. A diagnosis is then made following the detection of a homogeneous pattern of anti-nuclear antibody as well as autoantibodies against RNA. Which of the following types of RNA is most likely to be the target of the antibodies?
|Explanation=Antinuclear antibody (ANA) is a non-specific screening test to evaluate for the presence of rheumatic diseases. ANA screening often yields positive results in many connective tissue disorders and other autoimmune diseases, and may also be positive among normal individuals. Subtypes of antinuclear antibodies include anti-Smith (targets RNA) and anti-double stranded DNA (targets dsDNA) antibodies, both of which are associated with the diagnosis of systemic lupus erythematosus (SLE), and anti-histone antibodies (targets histones), which are associated with the diagnosis of drug-induced lupus.
|AnswerA=Messenger RNA (mRNA)
|AnswerAExp=Anti-Sm antibody does not target mRNA.

|AnswerB=Transfer RNA (tRNA)
|AnswerBExp=Anti-Sm antibody does not target tRNA.
|AnswerC=Ribosomal RNA (rRNA)
|AnswerCExp=Anti-Sm antibody does not target rRNA.
|AnswerD=Small nuclear ribonucleic acid (snRNA)
|AnswerDExp=Anti-Sm antibody is specific for SLE. Smith antigen is a group of proteins (B/D/E/F/G) without snRNA; it is metabolized by trypsin but not by RNase.
|AnswerE=Heterogeneous nuclear RNA (hnRNA)
|AnswerEExp=Anti-Sm antibody does not target hnRNA.
|EducationalObjectives=Subtypes of antinuclear antibodies include anti-Smith (targets RNA) and anti-double stranded DNA (targets dsDNA) antibodies, both of which are associated with the diagnosis of systemic lupus erythematosus (SLE), and anti-histone antibodies (targets histones), which are associated with the diagnosis of drug-induced lupus.
|References=Migliorini P, Baldini C, Rocchi V, et al. Anti-Sm and anti-RNP antibodies. Autoimmunity. 2005;38(1):47-54.<br>
First Aid 2015 page 213, 433.
|RightAnswer=D
|WBRKeyword=Small nuclear ribonucleic acid, snRNA, Antinuclear antibody, SLE, Systemic lupus erythematosus
|Approved=Yes
}}