MAP2K1 and familial atrioventricular septal defect: Mutations activating the mitogen-activated protein kinase pathway are found in more than 80% of patients with ECD, being Rapidly Accelerated Fibrosarcoma protein kinase (BRAF)V600E activating mutations in 57–70% of cases, and mitogen-activated protein kinase kinase 1 (MAP2K1) mutations in approximately 20% of cases [5].