Cardiovascular surgery in Marfan syndrome: implications of new molecular concepts in thoracic aortic disease

Acute dissection and rupture of aortic aneurysms comprise for 1-2% of all deaths in industrialized countries. Dilation of the aorta is caused by a multitude of mechanisms including inherited connective tissue disorders such as Marfan syndrome (MFS). MFS is one of the most common inherited connective tissue disorders affecting 1 in 5000 individuals. Although the phenotype of MFS can be quite variable, aneurysmal dilation of the aortic root and consecutive acute aortic dissection is the leading cause of death in this patient population. Over the past years it has been shown that a comprehensive understanding of this disorder provides greater understanding of vascular wall biology and identifies pathways relevant to aortic aneurysms and dissection in general. The current review discusses the surgical management of patients with MFS with a special emphasis on indications for surgery in this complex group of patients.

Acute aortic dissection determines the fate of initially untreated aortic segments in Marfan syndrome

The aim of the current study was to investigate incidence and causes of surgical interventions in primarily nontreated aortic segments after previous aortic repair in patients with Marfan syndrome.

Should aortic arch replacement be performed during initial surgery for aortic root aneurysm in patients with Marfan syndrome?

OBJECTIVES: The aim of this study was to investigate whether total arch replacement (TAR) during initial surgery for root aneurysm should be routinely performed in patients with Marfan syndrome (MFS). METHODS: Retrospective analysis of 94 consecutive MFS patients fulfilling Ghent criteria who underwent 148 aortic surgeries and were followed at this institution during the past 16 years. RESULTS: The mean follow-up interval was 8.8 ± 7 years. Initial presentation was acute aortic dissection (AAD) in 35% of patients (76% Type A and 24% Type B) and aneurismal disease in 65%. TAR was performed in 8% of patients during initial surgery for AAD (otherwise a hemi-arch replacement was performed) and 1.6% in elective root repair. Secondary TAR had to be performed in only 3% of patients without, but in 33% following AAD (33% Type A and 33% Type B; P = 0.0001). Thirty-day, 6-month, 1-year and overall mortalities were 3.2, 5.3, 6.4 and 11.7%, respectively. Operative and 30-day mortalities in secondary aortic arch replacement were zero. Secondary TAR after AAD did not increase the need for the replacement of the entire thoracoabdominal aorta during follow-up compared with patients without secondary TAR (37 vs 40%, P = 1.0). CONCLUSIONS: MFS patients undergoing elective root repair have small risk of reinterventions on the aortic arch, and primary prophylactic replacement does not seem to be justified. In patients with AAD, the need for reinterventions is precipitated by the dissection itself and not by limiting the procedure to the hemi-arch replacement in the emergency setting. Limiting surgery to the aortic root, ascending aorta and proximal aortic arch is associated with low mortality in MFS patients presenting with AAD.

Successful kidney transplantation from donor with Marfan's syndrome

Marfan's syndrome is caused by mutations in the extracellular matrix protein fibrillin-1 with aortic aneurysm and dissection being its most life-threatening manifestations. Kidney transplantation from donors with Marfan's syndrome has never been reported in the literature, possibly because of reticences due to the underlying connective tissue disease. Here, we report two patients with end-stage renal disease, transplanted with the kidneys from a donor with Marfan's syndrome who died of aortic dissection and cerebral hemorrhage. After delayed graft function in both recipients, renal function normalized with no renovascular complications and negative proteinuria for 6 years in one patient and 2 years in the other patient, who died from an ischemic cerebrovascular insult. Kidneys from organ donors with Marfan's syndrome might be suitable for transplantation.

Alterations of the thoracic spine in Marfan's syndrome

OBJECTIVE: The purpose of this study was to determine if the thoracic vertebral elements are altered in patients with Marfan's syndrome. MATERIALS AND METHODS: Thirty patients underwent helical CT of the thorax because of suspected thoracic aortic dilatation and acute dissection. Thirteen had Marfan's syndrome and 17 did not. Two reviewers, unaware of the final diagnosis, evaluated the images by consensus for laminar thickness, foraminal width, dural sac ratios, and vertebral scalloping for T2-T12. RESULTS: At T9-T12, dural sac ratios at the midcorpus level (p = 0.031) and foraminal width (p = 0.0124) were significantly greater in the patients with Marfan's syndrome than in the patients without. Dural sac ratios at lower endplate levels (p = 0.0685), laminar thickness (p = 0.951), and vertebral scalloping (p = 0.24) were not significantly greater in the patients with Marfan's syndrome than in the patients without. CONCLUSION: Because the phenotypic expression of Marfan's syndrome is variable, information on the spine from thoracic studies in combination with major criteria may be helpful clinically.

Identification and in silico analyses of novel TGFBR1 and TGFBR2 mutations in Marfan syndrome-related disorders

Very recently, heterozygous mutations in the genes encoding transforming growth factor beta receptors I (TGFBR1) and II (TGFBR2) have been reported in Loeys-Dietz aortic aneurysm syndrome (LDS). In addition, dominant TGFBR2 mutations have been identified in Marfan syndrome type 2 (MFS2) and familial thoracic aortic aneurysms and dissections (TAAD). In the past, mutations of these genes were associated with atherosclerosis and several human cancers. Here, we report a total of nine novel and one known heterozygous sequence variants in the TGFBR1 and TGFBR2 genes in nine of 70 unrelated individuals with MFS-like phenotypes who previously tested negative for mutations in the gene encoding the extracellular matrix protein fibrillin-1 (FBN1). To assess the pathogenic impact of these sequence variants, in silico analyses were performed by the PolyPhen, SIFT, and Fold-X algorithms and by means of a 3D homology model of the TGFBR2 kinase domain. Our results showed that in all but one of the patients the pathogenic effect of at least one sequence variant is highly probable (c.722C > T, c.799A > C, and c.1460G > A in TGFBR1 and c.773T > G, c.1106G > T, c.1159G > A, c.1181G > A, and c.1561T > C in TGFBR2). These deleterious alleles occurred de novo or segregated with the disease in the families, indicating a causative association between the sequence variants and clinical phenotypes. Since TGFBR2 mutations found in patients with MFS-related disorders cannot be distinguished from heterozygous TGFBR2 mutations reported in tumor samples, we emphasize the importance of segregation analysis in affected families. In order to be able to find the mutation that is indeed responsible for a MFS-related phenotype, we also propose that genetic testing for sequence alterations in TGFBR1 and TGFBR2 should be complemented by mutation screening of the FBN1 gene.

Large genomic fibrillin-1 (FBN1) gene deletions provide evidence for true haploinsufficiency in Marfan syndrome

Mutations in the FBN1 gene are the major cause of Marfan syndrome (MFS), an autosomal dominant connective tissue disorder, which displays variable manifestations in the cardiovascular, ocular, and skeletal systems. Current molecular genetic testing of FBN1 may miss mutations in the promoter region or in other noncoding sequences as well as partial or complete gene deletions and duplications. In this study, we tested for copy number variations by successively applying multiplex ligation-dependent probe amplification (MLPA) and the Affymetrix Human Mapping 500 K Array Set, which contains probes for approximately 500,000 single-nucleotide polymorphisms (SNPs) across the genome. By analyzing genomic DNA of 101 unrelated individuals with MFS or related phenotypes in whom standard genetic testing detected no mutation, we identified FBN1 deletions in two patients with MFS. Our high-resolution approach narrowed down the deletion breakpoints. Subsequent sequencing of the junctional fragments revealed the deletion sizes of 26,887 and 302,580 bp, respectively. Surprisingly, both deletions affect the putative regulatory and promoter region of the FBN1 gene, strongly indicating that they abolish transcription of the deleted allele. This expectation of complete loss of function of one allele, i.e. true haploinsufficiency, was confirmed by transcript analyses. Our findings not only emphasize the importance of screening for large genomic rearrangements in comprehensive genetic testing of FBN1 but, importantly, also extend the molecular etiology of MFS by providing hitherto unreported evidence that true haploinsufficiency is sufficient to cause MFS.

Recent advances in understanding Marfan syndrome: should we now treat surgical patients with losartan?

OBJECTIVE: Marfan syndrome is a systemic connective tissue disorder caused by mutations in the fibrillin-1 gene. It was originally believed that Marfan syndrome results exclusively from the production of abnormal fibrillin-1 that leads to structurally weaker connective tissue when incorporated into the extracellular matrix. This effect seemed to explain many of the clinical features of Marfan syndrome, including aortic root dilatation and acute aortic dissection, which represent the main causes of morbidity and mortality in Marfan syndrome. METHODS: Recent molecular studies, most based on genetically defined mouse models of Marfan syndrome, have challenged this paradigm. These studies established the critical contribution of fibrillin-1 haploinsufficiency and dysregulated transforming growth factor-beta signaling to disease progression. RESULTS: It seems that many manifestations of Marfan syndrome are less related to a primary structural deficiency of the tissues than to altered morphogenetic and homeostatic programs that are induced by altered transforming growth factor-beta signaling. Most important, transforming growth factor-beta antagonism, through transforming growth factor-beta neutralizing antibodies or losartan (an angiotensin II type 1 receptor antagonist), has been shown to prevent and possibly reverse aortic root dilatation, mitral valve prolapse, lung disease, and skeletal muscle dysfunction in a mouse model of Marfan syndrome. CONCLUSION: There are indicators that losartan, a drug widely used to treat arterial hypertension in humans, offers the first potential for primary prevention of clinical manifestations in Marfan syndrome.

Proteomic analysis in aortic media of patients with Marfan syndrome reveals increased activity of calpain 2 in aortic aneurysms

BACKGROUND: Marfan syndrome (MFS) is a heritable disorder of connective tissue, affecting principally skeletal, ocular, and cardiovascular systems. The most life-threatening manifestations are aortic aneurysm and dissection. We investigated changes in the proteome of aortic media in patients with and without MFS to gain insight into molecular mechanisms leading to aortic dilatation. METHODS AND RESULTS: Aortic samples were collected from 46 patients. Twenty-two patients suffered from MFS, 9 patients had bicuspid aortic valve, and 15 patients without connective tissue disorder served as controls. Aortic media was isolated and its proteome was analyzed in 12 patients with the use of 2-dimensional difference gel electrophoresis and mass spectrometry. We found higher amounts of filamin A C-terminal fragment, calponin 1, vinculin, microfibril-associated glycoprotein 4, and myosin-10 heavy chain in aortic media of MFS aneurysm samples than in controls. Regulation of filamin A C-terminal fragmentation was validated in all patient samples by immunoblotting. Cleavage of filamin A and the calpain substrate spectrin was increased in the MFS and bicuspid aortic valve groups. Extent of cleavage correlated positively with calpain 2 expression and negatively with the expression of its endogenous inhibitor calpastatin. CONCLUSIONS: Our observation demonstrates for the first time upregulation of the C-terminal fragment of filamin A in dilated aortic media of MFS and bicuspid aortic valve patients. In addition, our results present evidence that the cleavage of filamin A is highly likely the result of the protease calpain. Increased calpain activity might explain, at least in part, histological alterations in dilated aorta.

Circulating transforming growth factor-beta in Marfan syndrome

BACKGROUND: Marfan syndrome (MFS) is caused by mutations in the fibrillin-1 gene and dysregulation of transforming growth factor-beta (TGF-beta). Recent evidence suggests that losartan, an angiotensin II type 1 blocker that blunts TGF-beta activation, may be an effective treatment for MFS. We hypothesized that dysregulation of TGF-beta might be mirrored in circulating TGF-beta concentrations. METHODS AND RESULTS: Serum obtained from MFS mutant mice (Fbn1(C1039G/+)) treated with losartan was analyzed for circulating TGF-beta1 concentrations and compared with those from placebo-treated and wild-type mice. Aortic root size was measured by echocardiography. Data were validated in patients with MFS and healthy individuals. In mice, circulating total TGF-beta1 concentrations increased with age and were elevated in older untreated Fbn1(C1039G/+) mice compared with wild-type mice (P=0.01; n=16; mean+/-SEM, 115+/-8 ng/mL versus n=17; mean+/-SEM, 92+/-4 ng/mL). Losartan-treated Fbn1(C1039G/+) mice had lower total TGF-beta1 concentrations compared with age-matched Fbn1(C1039G/+) mice treated with placebo (P=0.01; n=18; 90+/-5 ng/mL), and circulating total TGF-beta1 levels were indistinguishable from those of age-matched wild-type mice (P=0.8). Correlation was observed between circulating TGF-beta1 levels and aortic root diameters in Fbn1(C1039G/+) and wild-type mice (P=0.002). In humans, circulating total TGF-beta1 concentrations were elevated in patients with MFS compared with control individuals (P<0.0001; n=53; 15+/-1.7 ng/mL versus n=74; 2.5+/-0.4 ng/mL). MFS patients treated with losartan (n=55) or beta-blocker (n=80) showed significantly lower total TGF-beta1 concentrations compared with untreated MFS patients (P< or =0.05). CONCLUSIONS: Circulating TGF-beta1 concentrations are elevated in MFS and decrease after administration of losartan, beta-blocker therapy, or both and therefore might serve as a prognostic and therapeutic marker in MFS.

Prospective risk stratification of sudden cardiac death in Marfan's syndrome.

BACKGROUND Marfan syndrome (MFS) is a variable, autosomal-dominant disorder of the connective tissue. In MFS serious ventricular arrhythmias and sudden cardiac death (SCD) can occur. The aim of this prospective study was to reveal underlying risk factors and to prospectively investigate the association between MFS and SCD in a long-term follow-up. METHODS 77 patients with MFS were included. At baseline serum N-terminal pro-brain natriuretic peptide (NT-proBNP), transthoracic echocardiogram, 12-lead resting ECG, signal-averaged ECG (SAECG) and a 24-h Holter ECG with time- and frequency domain analyses were performed. The primary composite endpoint was defined as SCD, ventricular tachycardia (VT), ventricular fibrillation (VF) or arrhythmogenic syncope. RESULTS The median follow-up (FU) time was 868 days. Among all risk stratification parameters, NT-proBNP remained the exclusive predictor (hazard ratio [HR]: 2.34, 95% confidence interval [CI]: 1.1 to 4.62, p=0.01) for the composite endpoint. With an optimal cut-off point at 214.3 pg/ml NT-proBNP predicted the composite primary endpoint accurately (AUC 0.936, p=0.00046, sensitivity 100%, specificity 79.0%). During FU, seven patients of Group 2 (NT-proBNP ≥ 214.3 pg/ml) reached the composite endpoint and 2 of these patients died due to SCD. In five patients, sustained VT was documented. All patients with a NT-proBNP<214.3 pg/ml (Group 1) experienced no events. Group 2 patients had a significantly higher risk of experiencing the composite endpoint (logrank-test, p<0.001). CONCLUSIONS In contrast to non-invasive electrocardiographic parameter, NT-proBNP independently predicts adverse arrhythmogenic events in patients with MFS.

Outcome of aortic surgery in patients with Loeys-Dietz syndrome primarily treated as having Marfan syndrome.

OBJECTIVES Loeys-Dietz syndrome (LDS) is characterized by acute aortic dissection (AAD) at aortic diameters below thresholds for intervention in patients with Marfan syndrome (MFS). The aim was to evaluate the outcome of LDS patients primarily treated as having MFS. METHODS We analysed 68 consecutive patients who underwent surgery between 1995 and 2007 under the assumption of having MFS before retrospectively being screened for LDS when genetic testing became available. These patients were followed up until 2013, and underwent a total of 115 aortic surgeries. RESULTS Genetic testing was performed in 76% of the patients. Sixty per cent of these patients were positive for FBN1 mutations associated with MFS, 20% had no FBN1 mutation and 17% harboured TGFBR1/2 mutations associated with LDS. Mean follow-up was 12.7 ± 7 years. All-cause 30-day, 6-month and 1-year mortality rates were 2.9, 4.4 and 7.3%, respectively. Interestingly, initial presentation with AAD did not differ between LDS and MFS (33 vs 37%, P = 0.48) nor did long-term mortality compared with MFS patients (11 vs 16%, P = 1.0) or within MFS subgroups (FBN1 positive 13%, P = 1.0; FBN1 negative 10%, P = 1.0; not tested 25%, P = 0.62). There was no difference in the need for secondary total arch replacement between LDS and MFS patients (11 vs 14%, P = 1.0), nor within MFS subgroups (FBN1 positive 16%, P = 1.0; FBN1 negative 10%, P = 1.0; not tested 13%, P = 1.0). Total aortic replacement became necessary in 22% of LDS compared with 12% of MFS patients (P = 0.6) and did not differ significantly between MFS subgroups. CONCLUSIONS Although early surgical intervention in LDS is warranted to avoid AAD, the current data suggest that once the diseased segment is repaired, there seems to be no additional burden in terms of mortality or reoperation rate compared with that in MFS patients, with or without confirmed FBN1 mutation.