Recently, several studies have demonstrated that blood GFAP levels measured by Simoa have potential as a useful NMOSD biomarker for (1) differentiating NMOSD from other demyelinating diseases, (2) identifying and predicting clinical attacks, (3) monitoring disease disability and progression, and (4) evaluating treatment effects (59, 71, 73–78) (Table 1). Here, GFAP is linked to demyelinating disease.