Mendelian randomization followed by single-cell RNA sequencing exploration identifies effector memory CD4+ T cells as a risk factor for myasthenia gravis.

Myasthenia gravis (MG) is an autoimmune neuromuscular junction disease classified as early onset MG (EOMG), which typically occurs before the age of 50 years, and late-onset MG (LOMG), which occurs after the age of 50 years. The contribution of different immune cell subsets to MG pathogenesis is not fully understood. To address this, we conducted 2-sample Mendelian randomization (MR) analyses incorporating 731 peripheral immunophenotypes associated with MG. To further explore cellular mechanisms, we analyzed an existing single-cell RNA sequencing (scRNA-seq) dataset derived from the peripheral blood of patients with MG during and after the myasthenic crisis phase. In MR analyses, IVW results suggested that 42 immunophenotypes were risk or protective factors for LOMG, whereas 28 immunophenotypes were involved in EOMG. Comprehensive sensitivity analyses confirmed the absence of heterogeneity and horizontal pleiotropy. Among these, the proportion of effector memory CD4 + T cells emerged as the most significant factor associated with an increased risk of LOMG. Single-cell analyses revealed an expansion of these cells in patients with LOMG during the myasthenic crisis stage compared with the stable stage, with functional annotations showing strong similarities to activated CD4 + T cells treated with TGF-β and IL-4. This study identified effector memory CD4 + T cells as a significant risk factor for LOMG through MR analyses and further explored an existing scRNA-seq dataset. The role of effector memory CD4 + T cells, potentially mediated by TGF-β and IL-4, in LOMG pathogenesis and disease exacerbation, highlighting the need for further functional studies.