Immunogenetics of Idiopathic Inflammatory Myopathies: The Role of HLA Genes Within and Beyond the Ancestral Haplotype

Idiopathic inflammatory myopathies constitute a group of immune-mediated disorders primarily affecting skeletal muscle, but they may also lead to significant involvement of internal organs. These conditions are highly heterogeneous, encompassing diverse clinical manifestations and multiple underlying pathophysiological mechanisms. A unifying feature across this disease spectrum is an autoimmune response characterized by the production of highly specific autoantibodies, which are detected in the majority of patients. Genetic studies have identified the principal susceptibility background as the 8.1 ancestral haplotype within the HLA region on chromosome 6. However, genetic predisposition extends beyond HLA loci and includes numerous genes encoding key molecules involved in cytokine production, the regulation of immune signaling pathways, and metabolic processes. In this paper, we review the currently identified genetic loci associated with inflammatory myopathies, with particular emphasis on the HLA system, as well as non-HLA genes and newly identified candidates.