The single nucleotide polymorphism site of aquaporin-4 gene in patients with neuromyelitis optica

The single nucleotide polymorphism (SNP) site within the aquaporin (AQP)-4 gene exons and its possible role in the pathogenesis of neuromyelitis optica (NMO) were studied. From March 2010 to June 2012, 72 patients with NMO from Xiangyang No. 1 People's Hospital, Hubei University of Medicine were enrolled in the NMO group. At the same time, 80 patients with multiple sclerosis (MS) were enrolled in our study as the MS group. Blood samples were collected and DNA was extracted for analysis of SNP sites of AQP4 gene. Specific site-directed mutagenesis method was used for site-directed mutagenesis on plasmid enhanced green fluorescence protein carrying AQP4 gene. Mutant plasmids were constructed and used for transfecting cell lines. The differences of anti-AQP4 antibody level in the cell line were analyzed. The possible correlation between AQP4 gene SNP sites and the pathogenesis of NMO were analyzed. In the NMO group, 6 SNP sites in AQP4 gene were located in exons 2 and 5. These included R108T, I110N, E280R, D281R, P295R and E317M. There was no SNP site in exons 1, 3 and 4. In the MS group, no SNP site was found in AQP4 gene. R108T, I110N, R108T/I110N, E280R/D281R, P295R and E317M cell lines were constructed in the NMO group, and anti-AQP4 antibody in the serum was compared between R108T/I110N, E280R/D281R and E317M cell lines and the original HEK293T cell line. The difference was statistically significant (P<0.05). The positive rate of anti-AQP4 antibody titer in serum was compared between R108T, I110N, R108T/I110N, E280R/D281R, P295R and E317M cell lines in the NMO group and the original cell line in the MS group. In conclusion, SNP sites in AQP4 gene in patients with NMO may lead to some conformational changes in AQP4 protein. This affects the antigenicity of AQP4 protein. The different intensity of antigen-antibody reaction may cause the differences of titer observed between the different mutant cell lines.