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Background: Preeclampsia is a major cause of maternal and perinatal mortality and morbidity. The etiology of preeclampsia remains unclear. Recently, it was shown that misregulation of fms-like tyrosine kinase-1 (Flt-1) in the peripheral blood mononuclear cells of pregnant women results in over-expression of the soluble splice variant of Flt-1, sFlt-1, producing an additional (extra-placental) source of sFlt-1 that can contribute to the etiology of preeclampsia. The aim of this study was to investigate the relationship between preeclampsia and a dinucleotide (threonine-glycine; TG)n repeat polymorphism in the 3' non-coding region of the Flt-1 gene., Methods: The number of the d(TG)n repeats was analyzed in 170 patients with preeclampsia and in 202 normotensive pregnancies. The region containing the dinucleotide repeat polymorphism of the Flt-1 gene was amplified by polymerase chain reaction (PCR) from the DNA samples and was analyzed by direct PCR sequencing., Results: We found 10 alleles of the dinucleotide repeat polymorphism and designated these as allele*12 (A1) through allele*23 (A12) according to the number of the TG repeats, from 12 to 23. The frequency of the 14-repeat allele (A3) was most abundant (63.82% in preeclampsia and 69.06% in controls), followed by the 21-repeat allele (A10; 28.53% in preeclampsia and 23.76% in controls). There was no significant difference in the allele frequency between patients with preeclampsia and normal controls. The most common genotype in preeclamptic and normotensive pregnancies was heterozygous (TG)14/(TG)21 (41.76%) and homozygous (TG)14/(TG)14 (45.05%), respectively. However, the genotype frequencies were not significantly different between preeclamptic patients and controls., Conclusion: This is the first study to characterize the dinucleotide repeat polymorphism of the Flt-1 gene in patients with preeclampsia. We found no differences in the allele or genotype frequencies between patients with preeclampsia and normal pregnancies. Although limited by a relatively small sample size, our study suggests that the d(TG)n repeat polymorphism of the Flt-1 gene is not associated with the development of preeclampsia in Korean pregnant women.