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.