Inflammatory myopathies (or idiopathic myositis) seem to arise, like other autoimmune diseases, on a predisposing genetic background. To assess the weight of genes, a team from the Karolinska Institutet in Stockholm used three national databases, exhaustive or nearly exhaustive, on the Swedish population, their family ties and their health care. It compared the 7,615 first-degree relatives of 1,620 myositis patients with 37,309 first-degree relatives of 7,797 myositis-free individuals. Released in July 2021, the results of this study show:
- an increased risk of having at least one first-degree relative with myositis for patients with the same pathology (adjusted odds ratio of 4.32),
- 22% heritability of myositis in all first-degree parents and 24% in siblings alone.
These results are superior to those of previous studies (5.5% for dermatomyositis in particular). Thus, the Swedish team suggests making a history of myositis in a first-degree relative an argument in favor of the diagnosis. They also encourage further research to identify new genetic factors of myositis. Past studies have already pointed out the potential role of certain HLA alleles (HLA-DRB1 * 03: 01 and HLA-B * 08: 01) or of the PTPN22 gene.
