Neuromyelitis optica (NMO) is a severe idiopathic inflammatory disease of the central nervous system primarily affecting the optic nerves and spinal cord. In this study, we generated genome-wide SNP data from NMO patients and normal controls (53 cases and 240 controls), and followed up on the association signals with samples from a larger number of inflammatory demyelinating diseases, including NMO (n=93), multiple sclerosis (MS, n=71), idiopathic recurrent transverse myelitis (IRTM, n=57), and normal controls (n=240). Statistical analyses revealed that a common promoter SNP in CYP7A1 has a protective/gene dose-dependent effect on the risk of NMO (P=0.0004). A stronger association between the variables and subsequently, a higher protective effect (lower OR) on the risk of NMO were observed among patients carrying the "G/G" genotype of rs3808607 than those with the "T/G" genotype (OR=0.38/P=0.01 vs. OR=0.12/P=0.0004, respectively). The associations which were only observed in patients with NMO suggest that there are differences in the genetic etiology of the inflammatory demyelinating diseases (NMO, classical MS, and IRTM).