U1 and systemic lupus erythematosus: Single ANA specificities are also adopted in the diagnosis of SLE and other systemic autoimmunity, e.g., anti-Smith (Sm) antigen (SLE), anti-Ro/SSA and anti-La/SSB (Sjogren’s syndrome or SjS), anti-U1-ribonucleoprotein (U1-snRNP) for mixed connective tissue disease (MCTD), and anti-topoisomerase I (Slc70) for systemic sclerosis (SSc) (8, 46, 52).