Our astrocyte-based CBA was negative in two patients previously diagnosed with AQP4+ NMOSD but tested negative (AQP4+ NMO #4) or with a low AQP4+ Ab titer (AQP4+ NMO #3; 1:32), a titer far higher than the one established in our assay (final serum concentration 15 μg/mL corresponding to a 1:860 dilution for this patient). This evidence concerns the gene AQP4 and neuromyelitis optica.