Thoracic endografting in a patient with hereditary hemorrhagic telangiectasia presenting with a descending thoracic aneurysm

SMAD4 gene mutation increases the risk of aortic dilation in patients with hereditary haemorrhagic telangiectasia

BACKGROUND

Mutations in the genes ENG, ACVRL1 and SMAD4 that are part of the transforming growth factor-beta signalling pathway cause hereditary haemorrhagic telangiectasia (HHT). Mutations in non-HHT genes within this same pathway have been found to associate with aortic dilation. Therefore, we investigated the presence of aortic dilation in a large cohort of HHT patients as compared to non-HHT controls.

METHODS

Chest computed tomography of consecutive HHT patients (ENG, ACVRL1 and SMAD4 mutation carriers) and non-HHT controls were reviewed. Aortic root dilation was defined as a z-score>1.96. Ascending and descending aorta dimensions were corrected for age, gender and body surface area.

RESULTS

In total 178 subjects (57.3% female, mean age 43.9±14.9years) were included (32 SMAD4, 47 ENG, 50 ACVRL1 mutation carriers and 49 non-HHT controls). Aortopathy was present in a total of 42 subjects (24% of total). Aortic root dilatation was found in 31% of SMAD4, 2% of ENG, 6% of ACVRL1 mutation carriers, and 4% in non-HHT controls (p<0.001). The aortic root diameter was 36.3±5.2mm in SMAD4 versus 32.7±3.9mm in the non-SMAD4 group (p=0.001). SMAD4 was an independent predictor for increased aortic root (β-coefficient 3.5, p<0.001) and ascending aorta diameter (β-coefficient 1.6, p=0.04).

CONCLUSIONS

SMAD4 gene mutation in HHT patients is independently associated with a higher risk of aortic root and ascending aortic dilation as compared to other HHT patients and non-HHT controls.

Prevalence of thoracic aortopathy in patients with juvenile Polyposis Syndrome-Hereditary Hemorrhagic Telangiectasia due to SMAD4

Hereditary hemorrhagic telangiectasia (HHT) is characterized by abnormal vascular structures that may present as epistaxis, telangiectasias, and/or arteriovenous malformations. The genes associated with HHT (ACVRL1, ENG, and SMAD4) are members of the TGFβ pathway. Other syndromes associated with abnormalities in TGFβ signaling include Marfan syndrome, Loeys-Dietz syndrome and related disorders. These disorders have aortic disease as a prominent finding. While there are case reports of patients with HHT and aortopathy (dilatation/aneurysm, dissection, and rupture), this has not been systematically investigated. We conducted a retrospective chart review to determine the prevalence of aortopathy in an HHT cohort. Patients from a single institution were identified who met the Curacao Criteria for a clinical diagnosis of HHT and/or had a mutation in ACVRL1, ENG, or SMAD4 and underwent echocardiogram. Two-dimensional echocardiograms were reviewed by a single pediatric cardiologist, and data were collected on demographics, genotype, HHT features, aortic root measurements, past medical history, and family history. Z scores and nomograms were utilized to identify abnormal results. Twenty-six patients from 15 families (one ACVRL1, four ENG, eight SMAD4, and two clinical diagnoses) were included in the analysis. Aortopathy was found in 6/26 (23%) patients; all had SMAD4 mutations. In our cohort, 6/16 (38%) SMAD4 mutation carriers had evidence of aortopathy. These data suggest that aortopathy could be part of the spectrum of SMAD4-induced HHT manifestations. Routine aortic imaging, including measurements of the aorta, should be considered in patients with SMAD4 mutations to allow for appropriate medical and surgical recommendations.

Development and pathologies of the arterial wall

Arteries consist of an inner single layer of endothelial cells surrounded by layers of smooth muscle and an outer adventitia. The majority of vascular developmental studies focus on the construction of endothelial networks through the process of angiogenesis. Although many devastating vascular diseases involve abnormalities in components of the smooth muscle and adventitia (i.e., the vascular wall), the morphogenesis of these layers has received relatively less attention. Here, we briefly review key elements underlying endothelial layer formation and then focus on vascular wall development, specifically on smooth muscle cell origins and differentiation, patterning of the vascular wall, and the role of extracellular matrix and adventitial progenitor cells. Finally, we discuss select human diseases characterized by marked vascular wall abnormalities. We propose that continuing to apply approaches from developmental biology to the study of vascular disease will stimulate important advancements in elucidating disease mechanism and devising novel therapeutic strategies.

Appreciating the broad clinical features of SMAD4 mutation carriers: a multicenter chart review

Heterozygous loss-of-function SMAD4 mutations are associated with juvenile polyposis syndrome and hereditary hemorrhagic telangiectasia. Some carriers exhibit symptoms of both conditions, leading to juvenile polyposis-hereditary hemorrhagic telangiectasia syndrome. Three families have been reported with connective tissue abnormalities. To better understand the spectrum and extent of clinical findings in SMAD4 carriers, medical records of 34 patients (20 families) from five clinical practices were reviewed. Twenty-one percent of the patients (7/34) had features suggesting a connective tissue defect: enlarged aortic root (n = 3), aortic and mitral insufficiency (n = 2), aortic dissection (n = 1), retinal detachment (n = 1), brain aneurysms (n = 1), and lax skin and joints (n = 1). Juvenile polyposis-specific findings were almost uniformly present but variable. Ninety-seven percent of the patients had colon polyps that were generally pan-colonic and of variable histology and number. Forty-eight percent of the patients (15/31) had extensive gastric polyposis. Hereditary hemorrhagic telangiectasia features, including epistaxis (19/31, 61%), mucocutaneous telangiectases (15/31, 48%), liver arteriovenous malformation (6/16, 38%), brain arteriovenous malformation (1/26, 4%), pulmonary arteriovenous malformation (9/17, 53%), and intrapulmonary shunting (14/23, 61%), were documented in 76% of the patients. SMAD4 carriers should be managed for juvenile polyposis and hereditary hemorrhagic telangiectasia because symptoms of both conditions are likely yet unpredictable. Connective tissue abnormalities are an emerging component of juvenile polyposis-hereditary hemorrhagic telangiectasia syndrome, and larger studies are needed to understand these manifestations.

Matrix-dependent perturbation of TGFβ signaling and disease

Transforming growth factor beta (TGFβ) is a multipotent cytokine that is sequestered in the extracellular matrix (ECM) through interactions with a number of ECM proteins. The ECM serves to concentrate latent TGFβ at sites of intended function, to influence the bioavailability and/or function of TGFβ activators, and perhaps to regulate the intrinsic performance of cell surface effectors of TGFβ signal propagation. The downstream consequences of TGFβ signaling cascades in turn provide feedback modulation of the ECM. This review covers recent examples of how genetic mutations in constituents of the ECM or TGFβ signaling cascade result in altered ECM homeostasis, cellular performance and ultimately disease, with an emphasis on emerging therapeutic strategies that seek to capitalize on this refined mechanistic understanding.

Lessons on the pathogenesis of aneurysm from heritable conditions

Aortic aneurysm is common, accounting for 1-2% of all deaths in industrialized countries. Early theories of the causes of human aneurysm mostly focused on inherited or acquired defects in components of the extracellular matrix in the aorta. Although several mutations in the genes encoding extracellular matrix proteins have been recognized, more recent discoveries have shown important perturbations in cytokine signalling cascades and intracellular components of the smooth muscle contractile apparatus. The modelling of single-gene heritable aneurysm disorders in mice has shown unexpected involvement of the transforming growth factor-β cytokine pathway in aortic aneurysm, highlighting the potential for new therapeutic strategies.

SMAD4 mutation segregating in a family with juvenile polyposis, aortopathy, and mitral valve dysfunction

Juvenile polyposis syndrome (JPS) is caused by heterozygous mutations in either SMAD4 or BMPR1A. Individuals with JPS due to mutations in SMAD4 are at greater risk to manifest signs of hereditary hemorrhagic telangiectasia (HHT). HHT is caused by either mutations in SMAD4 or other genes that modulate transforming growth factor-beta (TGFβ) signaling. Additional genes in the TGFβ network include FBN1, TGFBR1, and TGFBR2, mutations of which cause either Marfan syndrome (MFS) or Loeys-Dietz syndrome (LDS), respectively. As SMAD4, FBN1, and TGFBR1/2 map to different regions of the genome, disorders associated with mutations in these genes are not expected to co-segregate in a family. We report an individual whose family history was positive for aortopathy, mitral valve dysfunction, and JPS. Mutation analysis of SMAD4 implicates this gene for these phenotypes in this family. Although SMAD4 is among several genes in the TGFβ network, and although prior single case reports have described large vessel aneurysms in HHT, this is the first description of aortic and mitral disease presenting with JPS. This observation suggests that, in addition to HHT, individuals with SMAD4 mutations may be at risk for aortic dilation and mitral valve dysfunction. We emphasize the importance of comprehensive review of the medical history prior to molecular testing, especially in an asymptomatic patient.