Association between the single nucleotide polymorphism and the level of Aquaporin-4 protein expression in Han and minority Chinese with inflammatory demyelinating diseases of the central nervous system

The purpose of this study was to determine whether or not aquaporin-4 (AQP4) gene mutations are related to the pathogenesis of inflammatory demyelinating diseases in the central nervous system. Polymorphisms of AQP4 exons 1–5 were determined by sequencing DNA from 67 patients with central nervous system inflammatory demyelinating diseases, including neuromyelitis optica (NMO), multiple sclerosis, recurrent or simultaneous bilateral optic neuritis, and longitudinally extensive transverse myelitis. A plasmid with the identified new missense mutation was constructed, and human embryonic kidney cells (HEK293A) were transfected with either the pEGFP-N1-AQP4-M23 vector (bearing the identified mutated cDNA sequence) or with the plasmid bearing the wild-type AQP4 gene sequence. AQP4 protein expression was analyzed in both experimental groups using Western Blot analysis following protein extraction from transfected cells. A synonymous mutation (rs1839318) was detected on exon 3, and an additional synonymous mutation was detected on the exon 2-2 (rs72557968). Most importantly, a new missense mutation was detected on exon 2-1. According to Western blot analysis, the mutated cDNA sequence yielded increased AQP4 protein expression in comparison with the wild-type cDNA sequence (P < 0.05). AQP4 gene mutations are uncommon, occurring in only 3 out of 67 patients. Although it is possible that the mutations contributed to an increased risk of inflammatory central nervous system disease in these individuals, it is unlikely that mutations are a significant contributor to most patients with NMO spectrum disorders in China