Introduction: Mixed Connective Tissue Disease (MCTD) is a rare immune-mediated disorder characterized by overlapping features of juvenile idiopathic arthritis, systemic lupus erythematosus (SLE), systemic sclerosis, and dermatomyositis (DM)/polymyositis, associated with high titers of anti-U1 ribonucleoprotein antibodies (U1RNP). This evidence concerns the gene SNRNP70 and systemic lupus erythematosus.