Preventing a Catastrophe: Increasing Awareness of Loeys-Dietz Syndrome

Loeys-Dietz syndrome is a genetic disorder that predisposes patients to aortic aneurysms. If left untreated, the natural history of the associated aortopathy often culminates in fatal aortic dissection. We describe the case of a 21-year-old man who was diagnosed with Loeys-Dietz syndrome after 2 family members died of aortic dissection. This case highlights the importance of increased physician awareness of this syndrome, which can play a crucial role in preventing premature sudden cardiac death caused by aortic catastrophe.

Connective tissue disorders and cardiovascular complications: the indomitable role of transforming growth factor-beta signaling

Marfan Syndrome (MFS) and Loeys-Dietz Syndrome (LDS) represent heritable connective tissue disorders that cosegregate with a similar pattern of cardiovascular defects (thoracic aortic aneurysm, mitral valve prolapse/regurgitation, and aortic root 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. Given the evidence of increased transforming growth factor-beta (TGF-β) signaling in MFS and LDS, this signaling pathway may represent the common link in this relationship. To further explore this hypothetical link, this chapter will review the TGF-β signaling pathway, heritable connective tissue syndromes related to TGF-β receptor (TGFBR) mutations, and discuss the pathogenic contribution of TGF-β to these syndromes with a primary focus on the cardiovascular system.

Angiotensin II-dependent TGF-β signaling contributes to Loeys-Dietz syndrome vascular pathogenesis

Loeys-Dietz syndrome (LDS) is a connective tissue disorder that is characterized by a high risk for aneurysm and dissection throughout the arterial tree and phenotypically resembles Marfan syndrome. LDS is caused by heterozygous missense mutations in either TGF-β receptor gene (TGFBR1 or TGFBR2), which are predicted to result in diminished TGF-β signaling; however, aortic surgical samples from patients show evidence of paradoxically increased TGF-β signaling. We generated 2 knockin mouse strains with LDS mutations in either Tgfbr1 or Tgfbr2 and a transgenic mouse overexpressing mutant Tgfbr2. Knockin and transgenic mice, but not haploinsufficient animals, recapitulated the LDS phenotype. While heterozygous mutant cells had diminished signaling in response to exogenous TGF-β in vitro, they maintained normal levels of Smad2 phosphorylation under steady-state culture conditions, suggesting a chronic compensation. Analysis of TGF-β signaling in the aortic wall in vivo revealed progressive upregulation of Smad2 phosphorylation and TGF-β target gene output, which paralleled worsening of aneurysm pathology and coincided with upregulation of TGF-β1 ligand expression. Importantly, suppression of Smad2 phosphorylation and TGF-β1 expression correlated with the therapeutic efficacy of the angiotensin II type 1 receptor antagonist losartan. Together, these data suggest that increased TGF-β signaling contributes to postnatal aneurysm progression in LDS.

Loeys-Dietz syndrome: a Marfan-like syndrome associated with aggressive vasculopathy

Loeys-Dietz syndrome is a recently-characterised genetic disorder with an autosomal-dominant inheritance due to mutations in the transforming growth factor beta-receptor Type 1 or Type 2 genes. We present a Chinese female neonate with genetically-confirmed Loeys-Dietz syndrome, cleft palate, hypertelorism, and an early dilatation of the aortic root and ascending aorta. This syndrome is associated with an aggressive arteriopathy, with an increased risk of dissection and rupture. Early diagnosis, close monitoring and early surgery may prolong the life in affected individuals. Losartan is an emerging therapy that may help slow down the rate of arterial dilatation.