Contribution of germline and somatic mutations to risk of neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease characterized by optic neuritis and transverse myelitis, with an unclear genetic background. A genome-wide meta-analysis of NMOSD in Japanese individuals (240 patients and 50,578 controls) identified significant associations with the major histocompatibility complex region and a common variant close to CCR6 (rs12193698; p = 1.8 × 10^-8, odds ratio [OR] = 1.73). In single-cell RNA sequencing (scRNA-seq) analysis (25 patients and 101 controls), the CCR6 risk variant showed disease-specific expression quantitative trait loci effects in CD4⁺ T (CD4T) cell subsets. Furthermore, we detected somatic mosaic chromosomal alterations (mCAs) in various autoimmune diseases and found that mCAs increase the risk of NMOSD (OR = 3.37 for copy number alteration). In scRNA-seq data, CD4T cells with 21q loss, a recurrently observed somatic event in NMOSD, showed dysregulation of type I interferon-related genes. Our integrated study identified novel germline and somatic mutations associated with NMOSD pathogenesis.