Mixed Connective Tissue Disease (MCTD) is currently defined as an overlapping syndrome with clinical features of Systemic Sclerosis (SSc), Systemic Lupus Erythematosus (SLE), Rheumatoid arthritis (RA), and Polymyositis/Dermatomyositis (PM/DM); the presence of high-titer anti-ribonucleoprotein1 (U1RNP) or speckled anti-nuclear antibodies (ANA) at titer ≥1 : 2,000 is necessary for the diagnosis. This evidence concerns the gene BTG3 and systemic lupus erythematosus.