Elucidating genetic backgrounds of myasthenia gravis in Japanese by genome-wide association studies and multi-omics analyses of thymoma

Myasthenia gravis (MG) is an autoimmune disorder characterized by impaired neuromuscular transmission and motor symptoms. Its genetic background remains unclear, particularly beyond specific subtypes reported in European populations. Here, we perform a genome-wide association study (GWAS) of 1,434 MG cases covering all disease subtypes and 42,913 controls of Japanese, which newly identify the TERT locus (odds ratio [OR] = 1.31, P = 1.7×10^-10). Subtype-stratified GWASs show stronger signals for generalized MG (gMG; OR = 1.38, P = 1.6×10^-12), anti AChR antibody-positive gMG (g-AChR-Ab(+)MG; OR= 1.49, P = 2.1×10^-15), and thymoma-associated gMG (g-TAMG; OR = 1.92, P = 1.1×10^-15). Fine-mapping of the major histocompatibility complex region reveal distinct associations of HLA-DRB1 with late onset gMG (g-LOMG) and HLA-A with early onset gMG (g-EOMG). The MG risk TERT lead variant rs2736099 is associated with poor treatment response, especially in g-AChR-Ab(+)MG and g-EOMG (P < 0.0042). The biobank-based phenome-wide association study identify pleiotropic effects on lung cancer, hematological traits, and telomere length. Single cell transcriptomics and immunohistochemistry identified immature lymphocyte-specific TERT expression in thymoma specimens. Full-length transcriptomics reveal allele-specific decreasing effect of rs2736099-A on TERT expression. Our study unveils genetics of MG distinctly across disease subtypes, and involvement of TERT in its pathogenesis.