What Is the Frequency of “Truly” AQP4-IgG-Negative NMO and Does It Differ Phenotypically from Seropositive Disease? (P02.136)

OBJECTIVE: To investigate in patients fulfilling 1999 Wingerchuk diagnostic criteria for NMO: 1) the AQP4-IgG detection rate in recombinant antigen-based assays for sera scored negative by 1 st generation tissue-based indirect-immunofluorescence assay (IIF), and 2) the clinical characteristics of persistently seronegative patients. BACKGROUND: AQP4-IgG is a clinically validated biomarker unifying NMO spectrum disorders. Assay sensitivities/specificities vary. False negativity invalidates phenotype comparisons. DESIGN/METHODS: From 2005-2011, 5349 samples from Mayo Clinic patients were tested by IIF assay. Clinical records identified 159 patients with NMO. Of those, 109 (69%) were positive and 50 (31%) negative; 47 of the 50 sera scored negative were available for testing by ELISA (RSR/Kronus) and AQP4-transfected cell binding assays (CBA slides [Euroimmun] and in-house fluorescence-activated cell sorting [FACS]). Clinical and demographic characteristics were compared based on final serostatus. RESULTS: Thirty of the 47 IIF-negatives (64%) were re-classified seropositive. Overall, AQP4-IgG detection rate was improved to 88% by FACS assay, 85% by CBA and 80% by ELISA. For 24 of these 30 patients, serial specimens were available. Subsequent sera yielded a positive result in only 2 patients whose initial serum was negative by FACS assay: the 4 th of 6 specimens in one, and the subsequent 3 in the other. Of the 17 cases finally scored seronegative, only one specimen was available for 7, and 14 were receiving immunotherapy when blood was drawn. By comparison with seropositive cases, sexes were equally represented in seronegatives (female:male = 8:1 in seropositives; p CONCLUSIONS: Serological tests employing recombinant AQP4 antigen are significantly more sensitive than tissue-based IIF for NMO-IgG detection. Initial testing should be done before commencing immunotherapy and, if negative, a subsequent specimen tested. Patients seronegative by most sensitive (FACS) assay differ phenotypically from AQP4-IgG-seropositive patients. Supported by: Mayo Clinic Foundation, Guthy-Jackson Charitable Foundation (VL, CL, SP, BW, DW) and NIH (R01-NS65829, SP). Disclosure: Dr. Jiao has nothing to disclose. Dr. Fryer has nothing to disclose. Dr. Lennon stands to receive royalties for commercial assays to detect of aquaporin 4-specific autoan. Dr. Quek has nothing to disclose. Dr. McKeon has nothing to disclose. Dr. Costanzi has nothing to disclose. Dr. Iorio has nothing to disclose. Dr. Jenkins has nothing to disclose. Ms. Smith has received research support from Abbott Laboratories. Dr. Weinshenker has received personal compensation for activities with Novartis, Biogen Idec, Elan Corporation, GlaxoSmithKline Inc., Asahi Kasei Kuraray Medical Company as a consultant and/or participant on a data safety monitoring board. Dr. Weinshenker has received (royalty or license fee or contractual rights) payments from Mayo Medical Ventures. Dr. Wingerchuk has received research support from Genentech, Genzyme, Alexion, TerumoBCT and the Guthy-Jackson Charitable Foundation. Dr. Shuster has nothing to disclose. Dr. Lucchinetti stands to receive royalties for commercial assays to detect aquaporin 4-specific autoantibody. Dr. Pittock and Mayo Clinic have a financial interest in the technology entitled "Neuromyelitis Optica Autoantibodies as a Marker for Neoplasia." This technology has been licensed to a commercial entity but no royalties have been received. Dr Sean Pittock has received research support from Alexion Pharmaceuticals, Inc.