T cells specific for aquaporin 4, the major antigen of NMO, cross-react with the homologous ABC transporter peptide of Clostridium perfringens, suggesting that molecular mimicry against microbial antigens could induce the autoimmune response in NMO (Varrin-Doyer et al., 2012). The gene discussed is AQP4; the disease is neuromyelitis optica.