In particular, we have found significantly lower frequencies of CSF-restricted oligoclonal bands (OCBs) and other markers of intrathecal immunoglobulin G (IgG) synthesis in patients with aquaporin-4 (AQP4)-IgG-positive neuromyelitis optica (NMO) spectrum disorders (NMOSD), myelin oligodendrocyte glycoprotein antibody-associated encephalomyelitis (MOG-EM), acute demyelinating encephalomyelitis (ADEM) and paraneoplastic neurological disorders (PND) than in MS, as well as significant differences in intrathecal IgG composition and dynamics and in blood–CSF barrier function [2–13]. This evidence concerns the gene AQP4 and erythema multiforme.