AQP4 and neuromyelitis optica: Testing for rapid plasma reagin, cryoglobulins, hepatitis B and C, HIV, antinuclear antibody (ANA), antineutrophil cytoplasmic antibody, neuromyelitis optica/aquaporin 4 fluorescence-activated cell sorting, and myelin oligodendrocyte glycoprotein fluorescence-activated cell sorting returned negative results.