Surprisingly, with the exception of a deletion encompassing GATA4 seen in one trio subject and one singleton subject (Table 2), we did not discover de novo coding mutations or gene dosage alterations within the 59 trios in canonical AVSD genes (NKX2-5, EVC, CRELD1, GATA6) or at the newly discovered CHD risk locus NR2F2. This finding is consistent with studies of CHD examining candidate genes [39] and exome sequencing where protein-altering variants in any single gene are reported in no more than 1–4% of patients [7]. This evidence concerns the gene CRELD1 and familial atrioventricular septal defect.