Objective:To construct a fusion protein of extracellular domain peptide fragment of muscle specific kinase ( MuSK) and fluorescent protein mCherry ,and used as antigen in the detection of antibodies against MuSK ( MuSKAb ) in the sera of patients with myasthenia gravis ( MG).Methods:The mCherry gene was amplified by PCR from vector pRSET-B and cloned into pGEM-T Easy Vector,and furthermore, cloned into Eukaryotic expression vector pMT /BiP/V5-His ( MuSK), which contains MuSK extracellular domain 22-452 amino acid peptide fragment gene to construct the fluorescent fusion protein gene MuSK -mCherry.The recombinant vector was subsequently transfected into drosophila S 2 cells for expression.The expressed fusion proteins were verified in confocal mi-croscope ,and used as antigen in the detection of MuSKAb in sera of MG patents in fluorescence immunoprecipitation test .Results:The fluorescent fusion protein MuSK-mCherry was successfully constructed and expressed.The MuSKAb in sera of patents with MG could be detected in fluorescence immunoprecipitation test using the constructed MuSK-mCherry fusion protein as antigen.Conclusion: It is available to use the constructed fluorescent fusion protein MuSK-mCherry as antigen in fluorescence immunoprecipitation test for the detection of MuSKAb in sera of patents with MG.

Objective:To investigate the association of single nucleotide polymorphisms (SNPs) of receptor-associated protein at the synapse ( rapsyn ) with myasthenia gravis ( MG ).Methods: The genomic DNA was extracted from peripheral blood cells , sampled from 132 patients with MG and 153 control individuals.The 8 exons of rapsyn gene were amplified by PCR ,then the products of PCR sequenced directly.Each sequence was compared with wild-type rapsyn gene , and the association between mutation and clinical symptoms of MG analysed.Results:No mutation was found in the exons 1,2,4,5,6,7,and 8 of rapsyn gene both in MG patients and control group compared with the wild-type rapsyn gene.However,a new SNP,L222R[CTG>CGG(2)] or T665G,was found in exon-3.The allele and genotype frequencies of SNP L 222R met Hardy-Weinberg genetic equilibrium (P>0.05),indicating the group repre-sentativeness.The allele frequencies of G were not statistically different between patient and control groups ( P>0.05 ).There were differences in the 3 genotypes TT , TG and GG between patient ( 42.4% vs 48.5% vs 9.1%) and control ( 49.0% vs 33.3% vs 17.6%) groups ( P<0.05 ).The genotype frequencies of GG were statistically higher in control group than that in patient group , showing a recessive model of inheritance.Conclusion: The SNPs in the rapsyn gene are associated with MG in this study.L222R ( T665 G) is a new SNP found and allele G might be a protective factor for MG.