In the three index cases, we screened serum for the development of muscle specific immunoreactivity with standard-of-care immuno-blots against cN-1A, MDA-5, Tif1-gamma, NXP-2, SAE-1, Mi-2a, Mi-2b, Ku, PM-Scl 100, PM-Scl-75, Jo-1, SRP, PL-7, PL-12, EJ, OJ and Ro52—but there was no evidence of seropositivity, excluding development of antibodies toward common myositis antigens and suggestive of T cell-mediated toxicity. Here, TRIM33 is linked to myositis disease.