PDE9A and familial atrioventricular septal defect: The gene PDE9A, encoding a component of cGMP phosphodiesterase which further contributes to signal transduction by regulating the intracellular cyclic nucleotides’ concentration, has increased copy number in most patients with AVSD, consistent with our predicted rule (≥ −0.0164 and ≤ 0.075) [66,67].