In addition, using sera of patients with NMO and recombinant AQP4-specific monoclonal antibodies, Crane et al. [32] showed that AQP4-IgG monoclonal antibodies or their Fab fragments had consistently greater affinity for M23 than for M1 because of OAP assembly, again suggesting that the choice of AQP4 isoforms, and therefore OAP assembly, can directly influence assay sensitivity. Here, AQP4 is linked to neuromyelitis optica.