SHH and familial atrioventricular septal defect: Genetic studies indicate that AVSD is genetically heterogeneous, currently over 100 genetic mutations associated with AVSD have been identified, including VEGF-A pathway-related genes (COL6A1, COL6A2, CRELD1, FBLN2, FRZB) (Nguyen and Jay, 2014), SHH pathway-related genes (SHH) (Ackerman et al., 2012) and left-right patterning-related genes (ACVR2B, CFC1, FOXP1, LEFTY2, NODAL, ZIC3) (Alongi et al., 2020).