Loeys-Dietz syndrome is an autosomal dominant aortic aneurysm syndrome characterized by multisystemic involvement. The most typical clinical triad includes hypertelorism, bifid uvula or cleft palate and aortic aneurysm with tortuosity. Natural history is significant for aortic dissection at smaller aortic diameter and arterial aneurysms throughout the arterial tree. The genetic cause is heterogeneous and includes mutations in genes encoding for components of the transforming growth factor beta (TGFβ) signalling pathway: TGFBR1, TGFBR2, SMAD2, SMAD3, TGFB2 and TGFB3. Despite the loss of function nature of these mutations, the patient-derived aortic tissues show evidence of increased (rather than decreased) TGFβ signalling. These insights offer new options for therapeutic interventions.

Marfan Syndrome (MFS) and Loeys-Dietz Syndrome (LDS) represent heritable connective tissue disorders that segregate with a similar pattern of cardiovascular defects (thoracic aortic aneurysm, mitral valve prolapse/regurgitation, and aortic dilatation with regurgitation). This pattern of cardiovascular defects appears to be expressed along a spectrum of severity in many heritable connective tissue disorders and raises suspicion of a relationship between the normal development of connective tissues and the cardiovascular system. With overwhelming evidence of the involvement of aberrant Transforming Growth Factor-beta (TGF-β) signaling in MFS and LDS, this signaling pathway may represent the common link in the relationship between connective tissue disorders and their associated cardiovascular complications. To further explore this hypothetical link, this chapter will review the TGF-β signaling pathway, the heritable connective tissue syndromes related to aberrant TGF-β signaling, and will discuss the pathogenic contribution of TGF-β to these syndromes with a primary focus on the cardiovascular system.

Predominant cardiovascular manifestations in the spectrum of Heritable Thoracic Aortic Disease include by default aortic root aneurysms- and dissections, which may be associated with aortic valve disease. Mitral- and tricuspid valve prolapse are other commonly recognized features. Myocardial disease, characterized by heart failure and/or malignant arrhythmias has been reported in humans and in animal models harboring pathogenic variants in the Fibrillin1 gene. Description of clinical history of three cases from one family in Ghent (Belgium) and one family in St. Louis (US). We report on three cases from two families presenting end-stage heart failure (in two) and lethal arrhythmias associated with moderate left ventricular dilatation (in one). All three cases harbor a pathogenic variant in the SMAD3 gene, known to cause aneurysm osteoarthritis syndrome, Loeys-Dietz syndrome type 3 or isolated Heritable Thoracic Aortic Disease. These unusual presentations warrant awareness for myocardial disease in patients harboring pathogenic variants in genes causing Heritable Thoracic Aortic Disease and indicate the need for prospective studies in larger cohorts.

Aneurysm-osteoarthritis syndrome is a recently discovered inherited autosomal dominant connective tissue disease caused by SMAD3 mutations. Aneurysm-osteoarthritis syndrome is responsible for 2% of familial thoracic aortic aneurysms and dissections and is characterised by aneurysms, dissections, and tortuosity throughout the arterial tree in combination with osteoarthritis. Early-onset osteoarthritis is present in almost all patients. We present the case of a non-syndromic young boy with SMAD3 mutation isolated from the dilated aortic root and ascending aorta without osteoarthritis.

Spontaneous coronary artery dissection (SCAD) is an infrequent cause of acute coronary syndrome and is often underdiagnosed. Intramural hematoma is the most frequent angiographic presentation and is a challenging diagnosis that may require intravascular imaging techniques to confirm it and guide treatment. It affects mostly young women without coronary risk factors and is usually associated with fibromuscular dysplasia. SCAD has an underlying disease in 80% of patients. A SMAD3 mutation has been linked to aneurysm-osteoarthritis syndrome and has been identified as a cause of familial thoracic aortic aneurysm and dissection. The first reported case, to our knowledge, of a SMAD3 mutation underlying SCAD is described here.