The SspnKO genotype does not affect the incidences of ASD or membranous VSD in the Nkx2-5+/− mice, but Nkx2-5+/−/SspnKO double mutants have almost twice the incidence of muscular VSD compared to Nkx2-5+/− single mutants (Fig. 2). Here, NKX2-5 is linked to atrial septal defect.