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BACKGROUND: Tumor necrosis factor-a (TNF-a) is a multifunctional proinflammatory cytokine, associated with various inflammatory and autoimmune diseases. Elevated TNF-a levels in peritoneal fluid have been reported in women with endometriosis, suggesting that TNF-a may be involved in the development of endometriosis. In this study, we investigated the possible association between endometriosis and the TNF-a gene promoter polymorphisms -238G/A, -308G/A, -857C/T, -863C/A and -1031T/C in a Japanese population. METHODS: We compared the distribution of the -238G/A, -308G/A, -857C/T, -863C/A and -1031T/C polymorphisms in the promoter region of TNF-a in 130 endometriosis cases and 185 controls using PCRRFLP analysis. RESULTS: The allele frequencies of -238A, -308A, -857T, -863A and -1031C in controls were 2.0%, 1.3%, 19.4%, 17.0% and 18.6%, and in the cases 1.1%, 0.3%, 19.6%, 18.6% and 13.6%, respectively. No significant differences in frequencies were found between the crude endometriosis cases and controls. However, when the endometriosis group was divided into a subgroup of women with stage IV disease only, the frequency of the -1031C allele was significantly lower in this subgroup than controls. CONCLUSIONS: The variability of the -1031T/C polymorphism of the TNF-a gene may be associated with susceptibility to (AUTHOR: as meant?) endometriosis. [ABSTRACT FROM AUTHOR]