Mixed connective tissue disease (MCTD) is a rare systemic autoimmune disease characterized by the production of anti-U1 ribonucleoprotein (RNP) antibodies and the symptoms of several other systemic autoimmune diseases, including systemic lupus erythematosus (SLE), systemic sclerosis (SSc), rheumatoid arthritis, idiopathic inflammatory myopathy with Raynaud’s phenomenon, diffuse hand edema, polyarthritis, myositis, pleuritis, pericarditis, leukopenia, esophageal dysmotility, interstitial lung disease, and pulmonary hypertension1–3. Here, RNPC3 is linked to systemic lupus erythematosus.