In a study of complement in schizophrenia, SLE and Sjogren’s syndrome, it was suggested that C4 exhibited a sex-biased expression differences including in cerebrospinal fluid.58 We did not detect differential expression of C4 protein in EDTA-plasma between men and women among patients with IIM in this work or in previous studies.23 42 50 51 54 We did not detect differences in C4 GCN variations between female and male patients for DM, PM and JDM (online supplemental table S2). Here, C4A is linked to dermatomyositis.