The development of accessory pathways has been demonstrated in mice by using either activation of notch signaling or inactivation of Tbx2, indicating that dysregulation of the cell signaling pathways that are essential for the development of the AV canal and the AV node may be responsible for the Wolff-Parkinson-White syndrome.30,40 Tbx2 normally suppresses the expression of Cx40 and Cx34, and knockout of Tbx2 leads to the loss of the AV canal phenotype and high expression of Cx40 and Cx43 in an accessory pathway, allowing fast conduction between the atria and the ventricles.40 The gene discussed is TBX2; the disease is Wolff-Parkinson-White syndrome.