AQP4 and neuromyelitis optica: More recently, in a pathological case series of NMO versus MS lesions, Matsuoka et al. found significant variability in the degree of AQP4 loss in actively demyelinating lesions in between patients with NMO and significant lesion-to-lesion heterogeneity of AQP4 expression even in patients with preferential AQP4 loss.