TRIM21 and polymyositis: One such antibody, the anti-SS-A 52 kD IgG (also known as anti-Ro52), is the most common autoantibody detected in patients with idiopathic inflammatory myopathies (estimated to be present in 20–30% of dermatomyositis/polymyositis), and has been described to co-occur with myositis-specific antibodies, particularly the anti-synthetase antibodies and anti-MDA-5 [13–18].