Matiello et al. recently reported on 100 sporadic and 10 familial NMO cases (106 NMO-IgG seropositive); they detected mutations at Arg19 in 1.8% of NMO patients but not in control subjects.[34] These missense mutations occur within the 22 residues of genomic DNA that is unique to the AQP4 M1 isoform. This evidence concerns the gene AQP4 and neuromyelitis optica.