IFIH1 and dermatomyositis: Anti-MDA5 antibodies are one of the autoantibodies specific to dermatomyositis, discovered by Japanese researchers,1) and are known to be positive in around 20% of dermatomyositis cases.2–6) Anti-MDA5 antibody-positive dermatomyositis is known to be associated with a high frequency of rapidly progressive interstitial pneumonia, with few cutaneous and muscular symptoms, and has the poorest prognosis among interstitial pneumonia associated with dermatomyositis.