According to the Kahn criteria [4], the patient had a low titer of anti-RNP antibodies, no finger swelling, synovitis, myositis, or Raynaud’s phenomenon, and all of the autoimmune antibodies turned negative when the patient was seen again 2 months later, so the diagnosis of mixed connective tissue disease was not supported. The gene discussed is RNPC3; the disease is myositis disease.