Congenital heart disease (CHD) is the most common birth defect in humans. Genetic causes and underlying molecular mechanisms for CHD remain largely unknown. T-box transcription factor 3 (TBX3) plays a critical role in the developing heart in a dose-dependent manner. TBX3 represses chamber myocardial gene expression. Mutations in TBX3 gene have been associated to ulnar-mammary syndrome with multiple developmental defects, including cardiac defects. We hypothesized that the sequence variants within TBX3 gene promoter that change TBX3 levels may mediate CHD development. In this study, TBX3 gene promoter was genetically analyzed in large cohorts of patients with ventricular septal defect (VSD) (n=325) and ethnic-matched healthy controls (n=359). Seven sequence variants, including two single-nucleotide polymorphisms (g.3863 C>T and g.4095G>T), three novel deletions (g.4433_4435del, g.4672_4675del and g.4820_4821del) and two novel insertions (g.3913_3914ins and g.4735_4736ins), were identified. Five of the seven variants were identified in VSD patients and controls with similar frequencies. Two other variants were found only in controls. These variants, which were observed in high frequencies, did not modify or interrupt the critical binding site for basic transcription factors. Taken together, these results suggested that the sequence variants within the TBX3 gene promoter did not contribute to VSD etiology.
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