Given the causative role of the type I and II interferons in human autoimmune diseases, including their role in the initiation of the disease processes and in the molecular pathogenesis of connective tissue diseases [14,25,26], we decided to explore whether single nucleotide polymorphisms (SNPs) that are located in the IFN-A (encodes IFN-α), IFN-B (encodes IFN-β), and IFN-G (encodes IFN-γ) genes may also be associated with MCTD while using a case-control study. Here, IFNB1 is linked to mixed connective tissue disease.