By applying multiplex RT-qPCR, we assessed type I IFN activity by examining gene expression in peripheral blood mononuclear cells (PBMCs) obtained from patients with anti-MDA5+ DM to determine whether the IFN score could be used to differentiate anti-MDA5+ DM from other autoimmune diseases and different myopathy subtypes. This evidence concerns the gene IFNA1 and dermatomyositis.