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Interleukin-21 (IL-21) is a pleiotropic cytokine linking innate and adaptive immune responses, which has been reported to play a key role in multiple autoimmune diseases. The aim of the present case-control study was to investigate the genetic association between single nucleotide polymorphisms (SNPs) of rs907715 within the IL-21 gene and Graves' disease (GD) in a Southern Chinese population. A total of 211 patients with GD and 212 control subjects were recruited for the study. IL-21 gene rs907715 polymorphisms were detected by direct DNA sequencing. The results indicated that the frequencies of the GG genotype and the G allele in GD patients were significantly increased when compared with the frequencies in the controls (P=6.7×10-3 and P=2.0×10-5, respectively). In addition, the frequency of the AA genotype was much lower in the patient group when compared with the control group (16.6 vs. 34.0%; P=4.0×10-5). Furthermore, the G allele of rs907715 was associated with relapse in GD patients. These observations indicated that polymorphisms of IL-21/rs907715 may affect the susceptibility to GD in a Southern Chinese population. The G allele was significantly associated with an increased risk of GD development, whereas the A allele may lower the susceptibility to GD. [ABSTRACT FROM AUTHOR]