FOXC1 and Tetralogy of Fallot: If these variants result in a loss-of-function effect with incomplete penetrance, it could explain the more complex heart defects in some of our patients with larger deletions that included both FOXC1 and RREB1. However, patients with a FOXC1 variant have also been reported with a tetralogy of Fallot or a coarctation [63, 64].