have reduced digit number because of the early termination of Shh and FGF4 signaling. Ventricular septal defects This is a broad category encompassing many more specific congenital heart defects. Of those related to Tbx2, some are caused by duplication, or over expression, of Tbx2, and others are caused by deletion of the Tbx2 gene region. For example, patients with a duplication of the Tbx2 gene region have presented with atrioventricular abnormalities including: interventricular septal defect, patent foramen ovale, aortic coarctation, tricuspid valve insufficiency, and mitral valve stenosis. Contrary, those with Tbx2 gene deletion have presented with pulmonary hypertension and other heart defects, but is less reported. Role in tumorigenesis Tbx2 has been implicated in cancers associated with the lung, breast, bone, pancreas, and melanoma. It is known to be over-expressed in this group of cancers, altering cell-signaling pathways leading to tumorigenesis. Several pathways have been suggested and studied using mouse knockout models of genes within the signaling pathways. Currently, research using the knockout model of Tbx2 for study of tumorigenesis is limited. p14ARF/MDM2/p35/p21CIP1 Pathway. When up-regulated, Tbx2 inhibits p21CIP1. p21CIP1 is necessary for tissue senescence, and when compromised, leaves the tissue vulnerable to tumor-promoting signals. Wnt/beta-catenin Pathway. The role of Tbx2 in Wnt signaling has yet to be confirmed; however, up-regulation of Tbx2 in the beta-catenin signaling pathway leads to loss of the adhesion molecule E-cadherin. This returns cells to a mesenchymal state, and facilitates invasion of tumor cells. EGR1 Signaling Pathway. Finally, Tbx2 up-regulation increases its interaction with EGR1. EGR1 represses NDGR1 to increase cell proliferation, resulting in metastasis or tumor development. Together, the up-regulation of Tbx2 on these signaling pathways can lead to development of malignant tumors. Cancer treatment target Understanding the signaling pathways, and the role of Tbx2 in tumorigenesis, can aid in developing gene-targeted cancer treatments. Because Tbx2 is up-regulated in various types of cancer cells in multiple organ systems, the potential for gene therapy is optimistic. Scientists are interested in targeting a small domain of Tbx2 and Tbx3 to reduce its expression, and utilize small peptides known to suppress tumor genes to inhibit proliferation. An in vitro study using a cell line of human prostate cancer blocked endogenous Tbx2 using Tbx2 dominant-negative retroviral vectors found reduced tumor cell proliferation. Further, the same study suggests targeting WNT3A because of its role in cell-signaling with Tbx2, by utilizing a WNT antagonist such as SFRP-2. Because somatic cells