AbstractObjective. To determine the clinical, serologic, and immunogenetic correlations in patients with idiopathic inflammatory myopathies (IIM), and to evaluate the useful grouping of some diseases for practical clinical purposes.Methods. Patients with IIM were categorized according to clinical presentation as compared with auto‐antibody specificity. Serum samples from 84 patients were screened for myositis‐specific autoantibodies (MSAs) by indirect immunofluorescence and double immunodiffusion. All sera were also studied by protein A‐assisted immunoprecipitation. Genomic DNA was isolated from peripheral blood mononuclear cells, and HLA‐DQA1 and DRB1 alleles were determined. The patients were seen and followed up for many years in the same center.Results. MSAs were present in 19% of patients. The most common MSAs were antisynthetases in 13% of patients (Jo‐1 10.7%, PL‐12 1.2%, and EJ 1.2%), associated with the antisynthetase syndrome. Anti‐SRP was found in 1.2% of patients, associated with polymyositis, and anti‐Mi‐2 in 4.9%, found exclusively in patients with dermatomyositis. The most frequent MSA was PM‐Scl in 23.8% of patients, associated with scleromyositis, and Ku was present in 9.6% of patients with overlap syndromes. The alleles that were found at a significantly increased frequency were HLA‐DRB1*0301 (59.4%) and DQA1*0501 (71.6%), which are in linkage disequilibrium. DQA1*0501 was present in 85.7% of patients with antisynthetases, and in 100% of patients with PM‐Scl and Ku.Conclusion. The HLA‐DRB1*0301; DQA1*0501 haplotype was found to be significantly increased in this population overall and in those myositis patients with antisynthetase, anti‐PM‐ScI, and anti‐Ku antibodies. The results of this study confirm that IIM are heterogeneous syndromes, but can be divided into more useful groups on the basis of clinical, serolo
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