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{{WBRQuestion
|QuestionAuthor=Gerald Chi
|ExamType=USMLE Step 1
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathology
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Biochemistry, Pathology
|MainCategory=Biochemistry, Pathology
|SubCategory=Musculoskeletal/Rheumatology
|Prompt=A 37-year-old female presents with malaise, proxmial muscle weakness, and swollen hand and knee joints. She also reports dry eye and dry mouth. When exposed to cold temperatures, her fingers become pallor and cyanotic and turn red and tingle. Physical examination shows scaly erythematous eruptions overlying the knuckles and elbows. Laboratory findings include lymphopenia with mild anemia and thrombocytopenia. A diagnosis is made by the presence of speckled anti-nuclear antibody as well as of a certain type of autoantibodies against extractable nuclear antigens. Which of the following structures is most likely to be the target of the antibodies?

|Explanation=Mixed connective tissue disease combines features of scleroderma, myositis, systemic lupus erythematosus, and rheumatoid arthritis and is thus considered an overlap syndrome. MCTD commonly causes joint pain/swelling, malaise, Raynaud phenomenon, Sjögren's syndrome, muscle inflammation, and sclerodactyly. Distinguishing laboratory characteristics are a positive, speckled anti-nuclear antibody and an anti-U1-RNP antibody.
|AnswerA=Transfer RNA (tRNA)

|AnswerAExp='''Incorrect'''<BR>Anti-U1-RNP antibody does not target tRNA
|AnswerB=Small interfering RNA (siRNA) 

|AnswerBExp='''Incorrect'''<BR>Anti-U1-RNP antibody does not target siRNA
|AnswerC=Small nuclear ribonucleoprotein (snRNP)
|AnswerCExp='''Correct'''<BR>Anti-U1-RNP antibody targets snRNP, which is a complex of snRNA (produced by RNAP II) and multiple proteins.

|AnswerD=Heterogeneous nuclear RNA (hnRNA)

|AnswerDExp='''Incorrect'''<BR>Anti-U1-RNP antibody does not target hnRNA. The snRNP combines with hnRNA to form spliceosome and undergoes splicing.
|AnswerE=Deoxyribonucleic acid (DNA)

|AnswerEExp='''Incorrect'''<BR>Anti-U1-RNP antibody does not target DNA
|RightAnswer=C
|Approved=No
}}