Association between polymorphisms in the promoter region of T cell immunoglobulin and mucin domain-3 and myasthenia gravis-associated thymoma

Thymoma is a type of benign or low-grade malignant tumor, occurring on the thymic epithelium. Patients with thymoma may also suffer from myasthenia gravis (MG), presenting MG-associated thymoma. T cell immunoglobulin and mucin domain-3 (Tim-3), a subtype of the Tim protein family, may be an important immune regulatory and pivotal molecule associated with tumor development. In order to understand the etiology and pathogenesis of MG-associated thymoma in the Han population of North China, the present study investigated the association between a polymorphism on the −574 locus in the promoter of Tim-3 and the risk of MG-associated thymoma in the Han Chinese population. In total, 116 patients with thymoma and MG were enrolled into the MG-associated thymoma group, while 124 patients with thymoma, but without MG, were enrolled into the non-MG-associated thymoma group. Examinations were conducted to reach a definite diagnosis of thymoma and MG and rule out other autoimmune diseases. Allele-specific polymerase chain reaction (AS-PCR) was performed to determine the polymorphism on the −574 locus of Tim-3 in all the subjects. PCR products were randomly selected for sequencing. Statistically significant differences were detected between the distribution frequencies of the GT+TT genotype and T allele on the −574 locus of the MG-associated thymoma group (31.03 vs. 12.90%, respectively; χ(2)=11.609, P=0.001) and the non-MG-associated thymoma group (15.52 vs. 6.45%, respectively; χ(2)=10.198, P=0.001). In conclusion, the present study indicated that an association may exist between the polymorphism of the −574 locus in the Tim-3 promoter and MG-associated thymoma.