This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Anti U1-RNP antibody is seen in? 
Select and explain. 
A. SLE, B. Scleroderma, C. MCTD, D. Dermatomyositis
C: MCTD
Answer: C: MCTD 
Explanation: “Absence of U1 RNP antibodies essentially rules out mixed connective tissue disorder”
ANTINUCLEAR ANTIBODY (ANA) PATTERNS AND CLINICAL ASSOCIATIONS