Whereas homozygous or compound heterozygous loss-of-function variants in MYH11 cause MMIHS, heterozygous pathogenic variants account for 2% of Thoracic Aortic Aneurysm and Dissection (TAAD), and are also often associated with patent ductus arteriosus [47,68,117,118,119,120]. This evidence concerns the gene MYH11 and megacystis-microcolon-intestinal hypoperistalsis syndrome 1.