MCTD Defining Antibody — SCE Rheumatology MCQ

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EasyAutoimmune SerologyMCTD Defining AntibodySCE Rheumatology

A 45-year-old woman has Raynaud phenomenon, puffy hands, inflammatory polyarthritis and proximal muscle weakness, suggesting mixed connective tissue disease. Which autoantibody is the defining serological marker of this condition?

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Correct answer: A — Anti-U1 ribonucleoprotein (anti-U1 RNP)

Anti-U1 ribonucleoprotein (anti-U1 RNP) is the defining serological marker of mixed connective tissue disease and is usually present at high titre. It must be interpreted with a compatible clinical overlap phenotype; anti-U1 RNP can also occur in systemic lupus erythematosus and is not diagnostic in isolation. Anti-centromere is associated particularly with limited cutaneous systemic sclerosis, anti-dsDNA with SLE, anti-Jo-1 with antisynthetase syndrome, and anti-topoisomerase I with diffuse cutaneous systemic sclerosis and interstitial lung disease. Serial anti-U1 RNP titres are not established as a reliable measure of MCTD disease activity.

Reference: Ferrara R et al. Towards Early Diagnosis of Mixed Connective Tissue Disease: Updated Perspectives. ImmunoTargets and Therapy. 2023. https://pubmed.ncbi.nlm.nih.gov/37525698/