Therefore, the main objective of our study is to assess positivity for AQP4‐Ab in patients presenting with demyelinating inflammatory CNS diseases other than typical MS in Lithuania (an atypical course of MS; acute transverse myelitis [TM]; severe, atypical ON; NMO; acute disseminated encephalomyelitis [ADEM]; and clinically isolated syndrome [CIS]). This evidence concerns the gene AQP4 and neuromyelitis optica.