An 18-year-old female presents with transverse myelitis extending from T6 to the conus medullaris and recovers well following intravenous steroids. Retrospectively, she reports an episode suggestive of unilateral optic neuritis at age 16, with spontaneous recovery of visual acuity but with residual dyschromatopsia. Testing for AQP4-IgG results negative and a hypothesis of seronegative NMOSD is made, but she fails to meet the diagnostic criteria. Prednisone and azathioprine are started off-label. This evidence concerns the gene AQP4 and transverse myelitis.