To address these issues, we tested a large series of consecutive, paired CSF and serum samples from Caucasian patients with NMO or its formes frustes, longitudinally extensive transverse myelitis (LETM) or optic neuritis (ON), as well as from controls for AQP4-Ab using a recombinant cell based assay [14]. This evidence concerns the gene AQP4 and neuromyelitis optica.