In our index sample (sample 1A; see Table 1), from a patient with bilateral optic neuritis and longitudinally extensive transverse myelitis (negative oligoclonal bands in the cerebrospinal fluid [CSF], > 100 cells/μl CSF), a positive MOG-IgG result was obtained on testing by means of a fixed, Fcγ-specific cell-based assay (CBA) [15, 18] (Table 1). The gene discussed is MOG; the disease is optic neuritis.