The underlying diseases were idiopathic ON (n = 6), Bechet’s disease (n = 5), NMO (n = 3), systemic lupus erythematosus (SLE) (n = 2), sarcoidosis (n = 1), relapsing polychondritis (n = 1), and myeloperoxidase-anti-neutrophil cytoplasmic antibody-associated vasculitis (n = 1). The gene discussed is MPO; the disease is neuromyelitis optica.