As our testing methods for the autoantibody to Aquaporin 4 have been shown to be 76% sensitive and 100% specific, there exists a possibility that the ‘RION’ and ‘CRION’ cohorts within this study also contain NMO spectrum patients which may have reduced the differences in serum GFAP levels between the groups [19]. The gene discussed is GFAP; the disease is neuromyelitis optica.