While to our knowledge previously reported assays to detect anti-AQP4 antibodies in NMO rely either on microscopic observation of specific immune signals (visual fluorescence or colored precipitate), or on quantification of colorimetric, fluorescent or radioactive signals[25], the diagnostic assay we present takes into account both localization and magnitude of the fluorescent signal. The gene discussed is AQP4; the disease is neuromyelitis optica.