INTRODUCTION: Aortic aneurysms might represent life-threatening diseases, even though they are less common with respect to many other cardiovascular conditions. The global clinical awareness of aortic aneurysms, along with the latest methods of diagnosis, will definitely help reducing the morbidity and mortality associated with this condition. Genetic screening represents, at present, an emerging and helpful tool in supporting the clinical diagnosis of thoracic aortic aneurysms and/or dissection (TAA/D), a potential lethal condition with a rising incidence. Its clinical impact, as well as the therapeutic management, differs according to the syndromic or non-syndromic manifestations of the disease. TAA/D represents a characteristic clinical feature common to different connective tissue disorders, e.g., Marfan syndrome (MFS), Loeys-Dietz syndrome (LDS), and bicuspid aortic valve (BAV). Analysis of genes associated with these disorders helps in early detection of the disease and in differential diagnosis with important implications for the management of the individuals affected by these complex traits. PART I BACKGROUND: Genetic variants in transforming growth factor beta (TGF-β) receptors type 1 (TGFBR1) and type 2 (TGFBR2) genes have been associated with different hereditary connective tissue disorders sharing TAA/D. Mutations in both TGFBR1/2 genes have been described in patients with TAA/D and MFS, and they are consistently associated with LDS. Existing literature shows discordant data resulting from mutational screening of TGFBR1/2 genes in MFS patients. Aim of the first part of the PhD thesis was to investigate the role of TGFBR1/2 genetic variants in determining and/or modulating MFS clinical phenotype. MATERIALS AND METHODS: 75 unrelated patients who underwent FBN1 mutational screening (47 patients with pathogenetic and 28 without pathogenetic FBN1 mutation) were subjected to direct sequencing for TGFBR2/1genes. RESULTS: Forty-seven MFS patients (63%) carried a pathogenetic FBN1 mutation. No pathogenetic mutations were detected in TGFBR1/2 genes. Ten common polymorphisms were identified in TGFBR2 and 6 in TGFBR1. Their association with cardiovascular (CV) manifestations was evaluated. Carriers of A allele of rs11466512, delA allele of c.383delA or delT allele of c.1256-15del1T polymorphisms had a trend towards or significantly reduced Z-scores [2.2 (1.13-4.77); 2.1 (1.72-3.48); 2.5 (1.85-3.86)] with respect to homozygous wild-type MFS patients [4.20 (2.39-7.25); 3.9 (2.19-7.00); 3.9 (2.14-6.93)]. Carriers of A allele of rs2276767 polymorphism showed a trend towards increased Z-score [4.9 (2.14-7.16)] with respect to wild-type MFS patients [3.3 (1.75-5.45)]. The protective effect of TGFBR1/2 genetic score including all the 4 variants was also evaluated. MFS patients with 2 or more protective alleles included in the score had statistically significant reduced aortic Z-scores [2.20 (1.48-3.37)] with respect to patients with 1 or no protective alleles [4.20 (2.48-7.12)], p=0.007. Patients with severe aortic manifestations (aortic Z-score ≥2 or aortic surgery) showed a significantly lower prevalence of subjects with 2 or more protective alleles included in the genetic score (29.7%) than patients with no or milder CV involvement (63.6%, p=0.029). The genetic score protective effect on global aortic manifestations severity (aortic Z-score ≥2 or aortic surgery) was also observed at the logistic regression analysis adjusted for the presence of FBN1gene mutations [OR=0.21 (95% CI 0.05-0.84), p=0.028]. CONCLUSIONS: our data reappraise the role of TGFBR1 and TGFBR2 as major genes in MFS patients, while suggest that TGFBR1/2 genetic variants (in particular when evaluated as a burden by score) might play a role in modulating CV manifestation severity in MFS. PART II BACKGROUND: BAV is the most common congenital heart defect. Aortic dilatation is a common feature of BAV and an increased risk of aortic dissection has been reported, raising concerns for the proper timing of aortic surgery in these patients. Familial clustering has also been reported, mostly with an autosomal pattern of inheritance with reduced penetrance and variable expressivity. Actually, the heritability of BAV has been estimated to be 89%, thus suggesting the presence of a relevant genetic contribution. Furthermore, BAV has been described as an isolated trait or associated with other clinical manifestations in syndromic conditions, thus the identification of a syndromic condition in a BAV patient is clinically relevant in order to personalize indication to aortic surgery. Differences in the anatomic site of aortic wall vulnerability in MFS and BAV, were evidenced: the maximal aortic dilatation is observed at the level of the proximal thoracic ascending aorta in BAV patients, while it is mainly referred to the aortic root in MFS patients. Therefore, due to differences and similarities between BAV and MFS aortic wall pathology, the pathogenetic mechanisms underlying these conditions are still matter of debate. MATERIAL AND METHODS: 79 BAV patients were enrolled during the three years of the project. Fifteen out of the 79 BAV patients were analyzed by next generation sequencing (NGS). The NGS analysis available in the Center is a targeted sequencing of 91 genes known or with plausibility to be associated with connective tissue disorders. Whenever possible, we performed mutational screening on the first-degree family members of the probands (3 families). RESULTS: Data of this thesis on a cohort of 79 consecutive BAV patients confirmed that patients have a strong male predominance (~75%) and come to the attention of the cardiologists and have BAV diagnosis at a median age of 42 years. This datum underlines the usefulness in this moment of the patients clinical history for a differential diagnosis of the aortopathy that eventually accompanies the BAV diagnosis. In fact the identification of the presence of BAV in a patients with diagnosis of MFS as well as other related connective tissue disorders results in a different management of patients, in particular concerning the timing of aortic surgery. This issue is particular importance due to the fact that 1) in agreement with our and literature previous data, 46.7% of BAV patients in this study have Z-score ≥2 at the aortic root level; and 2) even if patients with ≥7 points of systemic score [calculated according to revised Ghent criteria] were significantly lower in BAV patients than in MFS patients or BAV/MFS patients, the analysis of systemic features showed that BAV patients have at least in part common systemic manifestations with MFS patients furtherly complicating, together with the possible presence of aortic aneurysm, the differential diagnosis between MFS and BAV. The targeted NGS approach, allowing the sequencing of coding region and adiacent regions of consensus for exon splicing of 91 genes (associated with MFS and related disorders, bicuspid aortic valve, aortopathies and aortcic wall remodeling), on the 15 BAV patients who underwent mutational screening identified 78 genetic variants with MAF<0.05 in the European populations (where available): 43 with a MAF<0.01 and 34 called damaging with at least 1 in silico prediction tool. Genes previously suspected to be associated with the disease (NOTCH1, FBN1, TGFB1) and genes not previously associated with the disease (LTBP1, 4) were identified, not all of them classified as damaging according to the applied in silico prediction tools. Family members of 3 probands were also analysed. In some cases, the pathogenetic mutation was detected in apparently healthy family members but not in the affected ones. CONCLUSIONS:data obtained in these first 3 analyzed families suggest that no major pathogenetic mutations in genes previously associated with BAV as well as in novel genes of the 91 included in our NGS panel are associated as major genetic determinants with this clinical phenotype in its isolated form as well as BAV/TAA. This datum together with those obtained in our 15 BAV patients and other previously commented literature data suggest that BAV often perceived as monogenic or oligogenic disorder might be declined as a complex multifactorial genetic trait due to the interaction of individual genetic profile, epigenetic effects, somatic mutations, and environmental factors.
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|Titolo:||Genetic bases of aortopathies: from Marfan syndrome to bicuspid aortic valve|
|Autore:||DE CARIO, Rosina|
|Citazione:||DE CARIO, R. (2017). Genetic bases of aortopathies: from Marfan syndrome to bicuspid aortic valve.|
|Appare nelle tipologie:||8.1 Tesi Dottorato|
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