A second locus for Marfan syndrome maps to chromosome 3p24.2-p25

The Molecular Genetics of Marfan Syndrome

Marfan syndrome (MFS) is a complex connective tissue disease that is primarily characterized by cardiovascular, ocular and skeletal systems disorders. Despite its rarity, MFS severely impacts the quality of life of the patients. It has been shown that molecular genetic factors serve critical roles in the pathogenesis of MFS. FBN1 is associated with MFS and the other genes such as FBN2, transforming growth factor beta (TGF-β) receptors (TGFBR1 and TGFBR2), latent TGF-β-binding protein 2 (LTBP2) and SKI, amongst others also have their associated syndromes, however high overlap may exist between these syndromes and MFS. Abnormalities in the TGF-β signaling pathway also contribute to the development of aneurysms in patients with MFS, although the detailed molecular mechanism remains unclear. Mutant FBN1 protein may cause unstableness in elastic structures, thereby perturbing the TGF-β signaling pathway, which regulates several processes in cells. Additionally, DNA methylation of FBN1 and histone acetylation in an MFS mouse model demonstrated that epigenetic factors play a regulatory role in MFS. The purpose of the present review is to provide an up-to-date understanding of MFS-related genes and relevant assessment technologies, with the aim of laying a foundation for the early diagnosis, consultation and treatment of MFS.

Marfan syndrome revisited: From genetics to the clinic

Marfan syndrome is an autosomal dominant connective tissue disease with an estimated incidence of 1 in 5000 individuals. In 90% of cases it is caused by mutations in the gene for fibrillin-1, the main constituent of extracellular microfibrils. Studies on animal models of Marfan syndrome have revealed that fibrillin-1 mutations interfere with local TGF-β signaling, in addition to impairing tissue integrity. The cardinal features involve the cardiovascular, ocular and skeletal systems. The diagnosis of Marfan syndrome is made according to the revised Ghent nosology. Early identification and appropriate management are critical for patients with Marfan syndrome, who are prone to the life-threatening cardiovascular complications of aortic aneurysms and aortic dissection. The standard treatment includes prophylactic beta-blockers in order to slow down dilation of the ascending aorta, and prophylactic aortic surgery. The success of current medical and surgical treatment of aortic disease in Marfan syndrome has substantially improved mean life expectancy, extending it above 72 years. This review aims to provide an overview of this hereditary disorder.

Fibrillin microfibrils and proteases, key integrators of fibrotic pathways

Supramolecular networks composed of multi-domain ECM proteins represent intricate cellular microenvironments which are required to balance tissue homeostasis and direct remodeling. Structural deficiency in ECM proteins results in imbalances in ECM-cell communication resulting often times in fibrotic reactions. To understand how individual components of the ECM integrate communication with the cell surface by presenting growth factors or providing fine-tuned biomechanical properties is mandatory for gaining a better understanding of disease mechanisms in the quest for new therapeutic approaches. Here we provide an overview about what we can learn from inherited connective tissue disorders caused primarily by mutations in fibrillin-1 and binding partners as well as by altered ECM processing leading to defined structural changes and similar functional knock-in mouse models. We will utilize this knowledge to propose new molecular hypotheses which should be tested in future studies.

High prevalence of ventricular repolarization abnormalities in people carrying TGFβR2 mutations

Mutations in the TGFβR2 gene have been associated with a life threatening risk of aortic dissection but no arrhythmic death has been previously reported. Two young females carrying a TGFβR2 mutation, initially diagnosed as Marfan syndrome or Loeys Dietz syndrome, presented sudden death with autopsy ruling out dissection. The ECGs of the 2 Sudden Cardiac Deaths revealed profound ventricular repolarization abnormalities with a sinusoidal T-U morphology associated with normal left ventricular ejection fraction. These data strongly suggest sudden cardiac arrhythmic deaths and prompted us to systematically study the repolarization pattern in the patients with TGFβR2 mutations. ECG findings from 58 mutation carriers patients (TGFβR2 group) were compared with those of 46 non-affected first degree relatives (control group). TGFβR2 mutation was associated with ventricular repolarization abnormalities in 47% of patients (p < 0.001 vs. controls), including a 19.6 ms (95%CI 8.7; 30.5) QTc interval prolongation compared to the non-affected first degree relatives (p < 0.001), higher prevalence of abnormal U waves (16% vs. 2%), and sinusoidal T-U morphology (10% vs. 0%). TGFβR2 mutations can be associated with abnormal ventricular repolarization pattern, longer QT interval than non-carrier relatives and an increased risk for sudden death.

Genetic Disorders of the Thoracic Aorta and Indications for Surgery

Genetic disorders of the aorta are rare but can lead to life-threatening thoracic aortic aneurysms. Although the genetic causes of many of these connective tissue diseases are well defined, others such as familial thoracic aortic aneurysm and bicuspid aortic valve aortopathy are not. The natural history of genetic thoracic aortic aneurysms is not well understood or predictable, and surgical guidelines for treatment remain imprecise. Future research should strive to provide in-depth and detailed genetic profiling to drive clinical management, including medical and surgical therapies.

A Decade of Discovery in the Genetic Understanding of Thoracic Aortic Disease

Aortic aneurysms are responsible for a significant number of all deaths in Western countries. In this review we provide a perspective on the important progress made over the past decade in the understanding of the genetics of this condition, with an emphasis on the more frequent forms of vascular smooth muscle and transforming growth factor β (TGF-β) signalling alterations. For several nonsyndromic and syndromic forms of thoracic aortic disease, a genetic basis has now been identified, with 3 main pathomechanisms that have emerged: perturbation of the TGF-β signalling pathway, disruption of the vascular smooth muscle cell (VSMC) contractile apparatus, and impairment of extracellular matrix synthesis. Because smooth muscle cells and proteins of the extracellular matrix directly regulate TGF-β signalling, this latter pathway emerges as a key component of thoracic aortic disease initiation and progression. These discoveries have revolutionized our understanding of thoracic aortic disease and provided inroads toward gene-specific stratification of treatment. Last, we outline how these genetic findings are translated into novel pharmaceutical approaches for thoracic aortic disease.

Pathophysiology and Japanese clinical characteristics in Marfan syndrome

Marfan syndrome is an autosomal dominant heritable disorder of the connective tissue, caused by mutations of the gene FBN1, which encodes fibrillin-1, a major component of the microfibrils of the extracellular matrix. Fibrillin-1 interacts with transforming growth factor-β (TGF-β), and dysregulated TGF-β signaling plays a major role in the development of connective tissue disease and familial aortic aneurysm and dissection, including Marfan syndrome. Losartan, an angiotensin II blocker, has the potential to reduce TGF-β signaling and is expected to be an additional therapeutic option. Clinical diagnosis is made using the Ghent nosology, which requires comprehensive patient assessment and has been proven to work well, but evaluation of some of the diagnostic criteria by a single physician is difficult and time-consuming. A Marfan clinic was established at the University of Tokyo Hospital in 2005, together with cardiologists, cardiac surgeons, pediatricians, orthopedists, and ophthalmologists in one place, for the purpose of speedy and accurate evaluation and diagnosis of Marfan syndrome. In this review, we discuss the recent progress in diagnosis and treatment of Marfan syndrome, and the characteristics of Japanese patients with Marfan syndrome.

Current evidence and insights about genetics in thoracic aorta disease

Thoracic aortic aneurysms have been historically considered to be caused by etiologic factors similar to those implied in abdominal aortic aneurysms. However, during the past decade, there has been increasing evidence that almost 20% of thoracic aortic aneurysms may be associated with a genetic disease, often within a syndromic or familial disorder. Moreover, the presence of congenital anomalies, such as bicuspid aortic valve, may have a unique common genetic underlying cause. Finally, also sporadic forms have been found to be potentially associated with genetic disorders, as highlighted by the analysis of rare variants and expression of specific microRNAs. We therefore sought to perform a comprehensive review of the role of genetic causes in the development of thoracic aortic aneurysms, by analyzing in detail the current evidence of genetic alterations in syndromes such as Marfan, Loeys-Dietz, and Ehler-Danlos, familial or sporadic forms, or forms associated with bicuspid aortic valve.

Relation between genotype and left-ventricular dilatation in patients with Marfan syndrome

Cardiovascular manifestations in patients with Marfan syndrome (MFS) are related to aortic and valvular abnormalities. However, dilatation of the left ventricle (LV) can occur, even in the absence of aortic surgery or valvular abnormalities. We evaluated genetic characteristics of patients with MFS with LV dilatation. One hundred eighty-two patients fulfilling the MFS criteria, without valvular abnormalities or previous aortic surgery, with a complete FBN1 analysis, were studied. FBN1 mutations were identified in over 81% of patients. Twenty-nine patients (16%) demonstrated LV dilatation (LV end diastolic diameter corrected for age and body surface area >112%). FBN1-positive patients carrying a non-missense mutation more often had LV dilatation than missense mutation carriers (14/74 versus 5/75; p<0.05). Finally, FBN1-negative MFS patients significantly more often demonstrated LV dilatation than FBN1-positive patients (10/33 versus 19/149; p<0.05). It is concluded that LV dilatation in MFS patients is more often seen in patients with a non-missense mutation and in those patients without an FBN1 mutation. Therefore physicians should be aware of the possibility of LV dilatation in these patients even in the absence of valvular pathology.

Biological features of thoracic aortic diseases. Where are we now, where are we heading to: established and emerging biomarkers and molecular pathways

Thoracic aortic aneurysms (TAAs) and aortic dissections (ADs) are among the main causes of mortality and morbidity in Western countries. For this reason, the diagnosis, prevention and prediction of TAAs and ADs have become a very active area of research; in fact, it is important to monitor and predict the evolution of these diseases over time. It is also critical, in cases of doubtful diagnosis, to receive some guidance from biochemical assays, particularly in the case of ADs. Although biological testing for disease prediction has already been discussed several times, the role of biomarkers in TAAs and ADs is still under discussion for routine patient screening, periodical follow-up or for prompt diagnosis in emergency conditions. In this review, we update the current knowledge and new trends regarding the role of biomarkers in thoracic aortic diseases, focusing on established and emerging biomarkers in the fields of genetics, inflammation, haemostasis and matrix remodelling as well as on substances released upon cell damage. Other than D-dimer, a sensitive but not a specific marker for the diagnosis of AD that has been widely tested by several authors and currently seems a viable option in ambiguous cases, the remaining markers have been most frequently assessed in limited or mixed patient populations. This currently precludes their widespread adoption as diagnostic or prognostic tools, even if many of these markers are conceptually promising. In years to come, we expect that future studies will further clarify the diagnostic and prognostic features of several established and emerging biomarkers that, to date, are still in the translational limbo separating biological discovery from a practical clinical role.

TGFBR3 variation is not a common cause of Marfan-like syndrome and Loeys-Dietz-like syndrome

Marfan syndrome (MFS) is caused by mutations in the fibrillin-1 (FBN1) gene, and mutations in FBN1 are known to be responsible for over 90% of all MFS cases. Locus heterogeneity has also been reported and confirmed, with mutations in the receptor genes TGFBR1 and TGFBR2 identified in association with MFS-related phenotypes. It is now known that dysregulation of TGF-ß signaling is involved in MFS pathogenesis. To test the hypothesis that dysregulation of TGFBR3-associated TGF-ß signaling is implicated in MFS or related phenotype pathogenesis, we selected a cohort of 49 patients, fulfilling or nearly fulfilling the diagnostic criteria for MFS. The patients were known not to carry a mutation in the FBN1 gene (including three 5' upstream alternatively spliced exons), the TGFBR1 and TGFBR2 genes. Mutation screening for the TGFBR3 gene in these patients and in controls led to the identification of a total of ten exonic (one novel), four intronic (one novel) and one 3'UTR variant in the TGFBR3 gene. Our data suggest that variations in TGFBR3 gene appear not to be associated with MFS or related phenotype.

Downregulation of transforming growth factor, beta receptor 2 and Notch signaling pathway in human abdominal aortic aneurysm

OBJECTIVE

Mutations in FBN1 and TGFBR2 genes are the main causative mutations identified in Marfan syndrome (MFS). The major vascular complication of MFS is aneurysm formation. Abdominal aortic aneurysm (AAA) is an acquired disease of later life of unknown etiology. The aim of this study was to examine if genetic aberrations in MFS-related genes FBN1 and TGFBR2 are present in patients with AAA.

METHODS

We assessed the presence of copy number variation (CNV) in FBN1 and TGFBR2 genes in AAA biopsies from twelve patients. We also analyzed the expression of these genes in AAA biopsies compared to control biopsies from six organ donors. In addition we assessed the expression of two members of the Notch signaling pathway NOTCH3 and HEY2 as well as aortic smooth muscle cell (AoSMC) differentiation marker TAGLN in AAA and control biopsies.

RESULTS

Loss of one copy (deletion) of the FBN1 exon 66 sequence and TGFBR2 exon 8 was identified in 7 (58%) and 11 (92%) of the 12 AAA biopsies. No copy number amplifications (duplications) were detected. Patients carrying TGFBR2 exon 8 deletion showed marked downregulation of this gene in AAA biopsies compared to control biopsies (0.699 vs. 1.765, p = 0.038). Notch signaling components NOTCH3 and HEY2 were markedly downregulated in AAA, while expression of the AoSMC differentiation marker TAGLN did not differ between AAA and control biopsies (0.468 vs. 0.486, p = 0.546).

CONCLUSION

This study suggests an acquired impairment in TGF-β signaling that along with downregulation of the Notch signaling pathway may contribute to the pathogenesis of AAA.

[Images in cardiology after clinical observation - aortic dissection in Marfan syndrome]

INTRODUCTION

Stanford type A aortic dissection is a rare phenomenon with high short-term mortality and clinical manifestations that can make differential diagnosis a lengthy process requiring several diagnostic examinations.

OBJECTIVES

Based on a case report, the aim is to highlight the importance of physical examination in the initial management of these patients and of rapid access to a surgical center. A brief review follows on the diagnosis and treatment of ascending aortic dissection, and its specific nature in Marfan syndrome.

CASE REPORT

A 33-year-old man was admitted to the emergency department of a district hospital with chest and back pain associated with vomiting, 20 hours after symptom onset. Initial physical examination revealed an aortic systolic murmur and musculoskeletal morphological abnormalities compatible with Marfan syndrome. Given suspected aortic dissection, a transthoracic echocardiogram was immediately performed, which showed an extensive intimal flap originating at the sinotubular junction. He was transferred to the cardiothoracic surgery department of a referral hospital where he was treated by a Bentall procedure.

CONCLUSION

In this case, careful physical examination during initial assessment raised the suspicion that this patient was in a high-risk group for aortic dissection, thus avoiding unnecessary and lengthy exams. This diagnosis requires emergent surgical treatment, and so direct contact in real time between those making in the diagnosis and the surgeon is essential, as well as protocols governing immediate access to a surgical center.

The role of the renin-angiotensin system in thoracic aortic aneurysms: clinical implications

Thoracic aortic aneurysms (TAAs) are a potential life-threatening disease with limited pharmacological treatment options. Current treatment options are aimed at lowering aortic hemodynamic stress, predominantly with β-adrenoceptor blockers. Increasing evidence supports a role for the renin-angiotensin system (RAS) in aneurysm development. RAS blockade would not only lower blood pressure, but might also target the molecular pathways involved in aneurysm formation, in particular the transforming growth factor-β and extracellular signal-regulated kinase 1/2 pathways. Indeed, the angiotensin II type 1 (AT₁) receptor blocker losartan was effective in lowering aortic root growth in mice and patients with Marfan's syndrome. RAS inhibition (currently possible at 3 levels, i.e. renin, ACE and the AT₁ receptor) is always accompanied by a rise in renin due to interference with the negative feedback loop between renin and angiotensin II. Only during AT₁ receptor blockade will this result in stimulation of the non-blocked angiotensin II type 2 (AT₂) receptor. This review summarizes the clinical aspects of TAAs, provides an overview of the current mouse models for TAAs, and focuses on the RAS as a new target for TAA treatment, discussing in particular the possibility that AT₂ receptor stimulation might be crucial in this regard. If true, this would imply that AT₁ receptor blockers (and not ACE inhibitors or renin inhibitors) should be the preferred treatment option for TAAs.

Genetic testing in aortic aneurysm disease: PRO

Thoracic aortic aneurysms leading to type A dissections (TAAD) are the major diseases affecting the aorta. A genetic predisposition for TAAD can occur as part of a genetic syndrome. It can be inherited in an autosomal dominant manner with decreased penetrance and variable expression. Genetic heterogeneity for familial TAAD has been demonstrated with the identification of four genes leading to TAAD. Genetic testing for TAAD and the phenotype and management of patients harboring mutations in these genes are addressed in this article.

Genetics of Moyamoya disease

Moyamoya disease (MMD) is a disease pattern consisting of bilateral stenosis of the intracranial internal carotid arteries (ICA) accompanied by a network of abnormal collateral vessels that bypass the stenosis. Once symptomatic, insufficient cerebral blood flow or rupture of the fragile collaterals may cause stroke or hemorrhage, resulting in severe neurological dysfunction or death. The etiology of MMD is still unknown, although few associations with other diseases and environmental factors have been described. Strong regional differences in epidemiological data, as well as known familial cases, turned the focus to genetics for the insight into the disease's pathogenesis. Thus far, several reports have suggested specific genetic loci and individual genes as predisposing to MMD, but none have demonstrated reproducible results in independent cohorts. Small sample sizes, as well as a likely multifactorial origin, seem to be the most challenging tasks in identifying the disease-causing mechanisms. Once identified, susceptibility genes may allow preventive screening and a possible development of novel therapeutic options.

A fourth locus for autosomal dominant hypercholesterolemia maps at 16q22.1

Autosomal dominant hypercholesterolemia (ADH) is characterized by isolated increase in plasmatic low-density lipoprotein (LDL) cholesterol levels associated with high risk of premature cardiovascular disease. Mutations in LDLR, APOB, and PCSK9 genes have been shown to cause ADH. We now report further genetic heterogeneity of ADH through the study of a large French family in which the involvement of these three genes was excluded. A genome-wide scan mapped the disease-causing gene, named HCHOLA4, at 16q22.1 in a 7.89-Mb interval containing 154 genes with a maximum LOD score of 3.9. To reduce the linked region, we genotyped 18 smaller non-LDLR/non-APOB/non-PCSK9-ADH families at the HCHOLA4 locus. Six families did not exclude linkage to the locus, but none allowed reduction of the disease interval. The 154 regional genes were sorted according to the function of the encoded protein and tissue expression profiles, and 57 genes were analyzed through sequencing of their coding region and close flanking intronic parts. No disease-causing mutation was identified in these families, particularly in the LCAT gene. Finally, our results also show the existence of other ADH genes as nine families were neither linked to LDLR, APOB, and PCSK9 genes nor to the new HCHOLA4 locus.

Marfan syndrome. Part 1: pathophysiology and diagnosis

Marfan syndrome is a connective-tissue disease inherited in an autosomal dominant manner and caused mainly by mutations in the gene FBN1. This gene encodes fibrillin-1, a glycoprotein that is the main constituent of the microfibrils of the extracellular matrix. Most mutations are unique and affect a single amino acid of the protein. Reduced or abnormal fibrillin-1 leads to tissue weakness, increased transforming growth factor beta signaling, loss of cell-matrix interactions, and, finally, to the different phenotypic manifestations of Marfan syndrome. Since the description of FBN1 as the gene affected in patients with this disorder, great advances have been made in the understanding of its pathogenesis. The development of several mouse models has also been crucial to our increased understanding of this disease, which is likely to change the treatment and the prognosis of patients in the coming years. Among the many different clinical manifestations of Marfan syndrome, cardiovascular involvement deserves special consideration, owing to its impact on prognosis. However, the diagnosis of patients with Marfan syndrome should be made according to Ghent criteria and requires a comprehensive clinical assessment of multiple organ systems. Genetic testing can be useful in the diagnosis of selected cases.

The Marfan syndrome: implications for athletes and their echocardiographic assessment

Sudden death of competitive athletes is rare. These deaths challenge the perception that trained athletes represent the healthiest segment of modern society. The increasing frequency of such reported deaths worldwide and the visibility of the issue is underlined by the high-profile nature of each case. The majority of these deaths have been due to a variety of undiagnosed cardiovascular diseases. Marfan syndrome is a heritable disorder of the connective tissue that can hold life threatening consequences, especially for the athletic population. This paper will aim to review cardiovascular pathophysiology and assessment in relation to Marfan syndrome with particular reference to echocardiography and the athletic population.

Comparison of Clinical Presentations and Outcomes Between Patients With TGFBR2 and FBN1 Mutations in Marfan Syndrome and Related Disorders

Background— TGFBR2 mutations were recognized recently among patients with a Marfan-like phenotype. The associated clinical and prognostic spectra remain unclear.

Methods and Results— Clinical features and outcomes of 71 patients with a TGFBR2 mutation (TGFBR2 group) were compared with 50 age- and sex-matched unaffected family members (control subjects) and 243 patients harboring FBN1 mutations (FBN1 group). Aortic dilatation was present in a similar proportion of patients in both the TGFBR2 and FBN1 groups (78% versus 79%, respectively) but was highly variable. The incidence and average age for thoracic aortic surgery (31% versus 27% and 35±16 versus 39±13 years, respectively) and aortic dissection (14% versus 10% and 38±12 versus 39±9 years) were also similar in the 2 groups. Mitral valve involvement (myxomatous, prolapse, mitral regurgitation) was less frequent in the TGFBR2 than in the FBN1 group (all P <0.05). Aortic dilatation, dissection, or sudden death was the index event leading to genetic diagnosis in 65% of families with TGFBR2 mutations, versus 32% with FBN1 mutations ( P =0.002). The rate of death was greater in TGFBR2 families before diagnosis but similar once the disease had been recognized. Most pregnancies were uneventful (without death or aortic dissection) in both TGFBR2 and FBN1 families (38 of 39 versus 213 of 217; P =1). Seven patients (10%) with a TGFBR2 mutation fulfilled international criteria for Marfan syndrome, 3 of whom presented with features specific for Loeys-Dietz syndrome.

Conclusions— Clinical outcomes appear similar between treated patients with TGFBR2 mutations and individuals with FBN1 mutations. Prognosis depends on clinical disease expression and treatment rather than simply the presence of a TGFBR2 gene mutation.

Understanding and treating moyamoya disease in children

Moyamoya disease, a known cause of pediatric stroke, is an unremitting cerebrovascular occlusive disorder of unknown etiology that can lead to devastating, permanent neurological disability if left untreated. It is characterized by progressive stenosis of the intracranial internal carotid arteries and their distal branches and the nearly simultaneous appearance of basal arterial collateral vessels that vascularize hypoperfused brain distal to the occluded vessels. Moyamoya disease may be idiopathic or may occur in association with other syndromes. Most children with moyamoya disease present with recurrent transient ischemic attacks or strokes. Although there is no definitive medical treatment, numerous direct and indirect revascularization procedures have been used to improve the compromised cerebral circulation, with outcomes varying according to procedure type. Such techniques improve the long-term outcome of patients with both idiopathic and syndrome-associated moyamoya disease. This review provides a comprehensive discussion of moyamoya disease in children, with an emphasis on the most effective surgical treatment options.

Transforming growth factor-beta signaling in thoracic aortic aneurysm development: a paradox in pathogenesis

Thoracic aortic aneurysms (TAAs) are potentially devastating, and due to their asymptomatic behavior, pose a serious health risk characterized by the lack of medical treatment options and high rates of surgical morbidity and mortality. Independent of the inciting stimuli (biochemical/mechanical), TAA development proceeds by a multifactorial process influenced by both cellular and extracellular mechanisms, resulting in alterations of the structure and composition of the vascular extracellular matrix (ECM). While the role of enhanced ECM proteolysis in TAA formation remains undisputed, little attention has been focused on the upstream signaling events that drive the remodeling process. Recent evidence highlighting the dysregulation of transforming growth factor-beta (TGF-beta) signaling in ascending TAAs from Marfan syndrome patients has stimulated an interest in this intracellular signaling pathway. However, paradoxical discoveries have implicated both enhanced TGF-beta signaling and loss of function TGF-beta receptor mutations, in aneurysm formation; obfuscating a clear functional role for TGF-beta in aneurysm development. In an effort to elucidate this subject, TGF-beta signaling and its role in vascular remodeling and pathology will be reviewed, with the aim of identifying potential mechanisms of how TGF-beta signaling may contribute to the formation and progression of TAA.

Marfan syndrome type II: there is more to Marfan syndrome than fibrillin 1

Marfan syndrome is a well-described autosomal dominant syndrome with widely variable clinical manifestations. Cardiovascular complications include mitral valve prolapse with or without associated mitral valve insufficiency, aortic root dilatation, and most importantly the occasional development of aortic aneurysms or rupture. Given the inconsistent phenotype along with the potentially life-threatening implications, clinicians are increasingly turning to genetic testing for definitive diagnostic confirmation. It has been well established that mutations in the FBN1 gene encoding the structural protein Fibrillin 1 is the molecular etiology of Marfan syndrome. However, there are numerous patients who meet the Ghent clinical diagnostic criteria for Marfan syndrome who do not have identifiable FBN1 mutations. Recently, mutations in TGFBR1 and TGFBR2 (transforming growth factor beta receptors 1 and 2, respectively) have been shown to result in Loeys-Dietz syndrome, a connective tissue disorder with significant phenotypic overlap with Marfan syndrome. Individuals with this Marfanoid disorder lack the ocular findings of Marfan syndrome and often have dysmorphic features such as unusual facies, cleft palate, and contractures. In addition, Loeys-Dietz syndrome patients often present in childhood with significant cardiovascular problems. This article serves to report an illustrative case of Loeys-Dietz syndrome and reviews the phenotypic consequences of FBN1 and TGFBR1 and TGFBR2 gene mutations.

In Vivo Corneal Confocal Microscopy in Marfan Syndrome

PURPOSE

To examine the cornea of patients with Marfan syndrome in comparison with a control group by using the in vivo confocal microscope.

METHODS

Twenty-four eyes of 12 patients with Marfan syndrome had their corneas examined using the in vivo confocal microscope Heidelberg Retina Tomograph (HRT) II/Rostock Cornea Module. The control group included 24 eyes of 12 subjects who had their corneas examined by the same in vivo confocal microscope.

RESULTS

Epithelium and neural plexus examination did not show any difference between the 2 groups. Examination of the stroma showed no significant differences concerning the morphology and density of keratocytes. The extracellular matrix of 16 of the 24 eyes of the Marfan group was clearly visible and showed thin highly reflective interconnected lines between keratocytes. In the healthy eye group, reflective lines were observed in only 5 of the 24 eyes. The endothelium of 14 corneas of the Marfan group showed brightly reflective particles. In no cornea of the control group were such particles observed.

CONCLUSIONS

Highly reflective extracellular matrix of the stroma and brightly reflective particles among the endothelial cells were the 2 main corneal findings observed by using in vivo corneal confocal microscopy in patients with Marfan syndrome compared with a control group. Further studies need to be made to confirm these findings and eventually find new criteria for Marfan syndrome from the examination of in vivo corneal confocal microscopy.

A comparison of genetic chromosomal loci for intracranial, thoracic aortic, and abdominal aortic aneurysms in search of common genetic risk factors

BACKGROUND

Genetic factors are likely to be involved in the pathogenesis of intracranial, ascending thoracic aorta, and infrarenal aortic abdominal aneurysms. Common genetic risk factors for these three types of aneurysms have been suggested. This review describes the results of whole-genome linkage studies on intracranial, thoracic aorta, and aortic abdominal aneurysms, and compares the genomic loci identified in these studies in search of possible common genetic risk factors for the three aneurysmal types.

METHODS

A literature search of all whole-genome linkage studies performed on intracranial, thoracic aorta, and aortic abdominal aneurysms was performed. The genomic loci identified in these studies were described and compared in search of similarities between them.

RESULTS

Five chromosomal regions on 3p24-25, 4q32-34, 5q, 11q24, and 19q that may play a role in the pathogenesis of two or more aneurysmal types were identified: 3p24-25 for thoracic aorta and intracranial aneurysms; 4q32-34 for aortic abdominal and intracranial aneurysms; 5q for thoracic aorta and intracranial aneurysms; 11q24 for thoracic aorta, aortic abdominal, and intracranial aneurysms; and 19q for aortic abdominal and intracranial aneurysms.

CONCLUSIONS

Five chromosomal regions that may include common genetic factors for intracranial, thoracic aorta, and aortic abdominal aneurysms were identified. Further studies are needed to explore these chromosomal regions in different aneurysm patient groups and may further help to unravel the disease pathogenesis of aneurysms in general.

Surgery Insight: the dilated ascending aorta—indications for surgical intervention

Awareness of the clinical significance of thoracic aortic aneurismal disease has increased in recent years. As diagnostic tools have improved our ability to identify aortic pathology, surgical outcomes have also improved, making intervention a life-saving option in the majority of cases. Here, we aim to examine the indications for surgical intervention on the dilated aorta, particularly the ascending segment. Studies of the natural history of ascending aortic aneurysms indicate that aneurysms exceeding 6 cm in maximum diameter are associated with a particularly high risk of complications. In the interest of providing some margin of safety, most surgeons would agree that intervention is indicated with an aortic diameter of 5.5 cm. Many would intervene even earlier (at 5.0 cm) for patients at low surgical risk, or for those with known connective tissue disorders such as Marfan's syndrome. In some cases, only the ascending aortic segment needs to be treated, while in others full root replacement is required. Reduction aortoplasty has been superseded largely by interposition graft replacement. The standard procedure involves replacement of the valve and root with a composite mechanical conduit or tissue root prosthesis, and results are excellent. Recently developed valve-sparing root reconstructive options, however, are promising and have encouraged an even more aggressive surgical stance.

Molecular Diagnoses and Treatments—Past, Present, or Future?

Use of molecular tools to diagnose and treat aortic disease, in particular, aortic aneurysms and aortic dissections, is still in its infancy, with great advancements expected in the future. Currently under investigation are the genetic markers linked to aortic disease that may help to identify patients at risk for their development prior to clinical presentation. In addition, specific gene defects may be identified that can assist in the understanding of the basic mechanisms contributing to development of aortic disease. Biomarkers are under investigation that can be used to monitor the development, progression, and possible response to therapy for aortic aneurysms and acute aortic syndromes. Equally important, further investigations into the molecular mechanisms involved in aortic pathology will result in increased understanding of the disease etiology and will lead to development of alternate therapies for these diseases prior to their catastrophic development. With advances in molecular technology, the molecular diagnosis and treatment of aortic diseases will begin to expand at a rapid rate and provide unique, improved therapies.

Severe aortic and arterial aneurysms associated with a TGFBR2 mutation

BACKGROUND

A 24-year-old man presented with previously diagnosed Marfan's syndrome. Since the age of 9 years, he had undergone eight cardiovascular procedures to treat rapidly progressive aneurysms, dissection and tortuous vascular disease involving the aortic root and arch, the thoracoabdominal aorta, and brachiocephalic, vertebral, internal thoracic and superior mesenteric arteries. Throughout this extensive series of cardiovascular surgical repairs, he recovered without stroke, paraplegia or renal impairment.

INVESTIGATIONS

CT scans, arteriogram, genetic mutation screening of transforming growth factor beta receptors 1 and 2.

DIAGNOSIS

Diffuse and rapidly progressing vascular disease in a patient who met the diagnostic criteria for Marfan's syndrome, but was later rediagnosed with Loeys-Dietz syndrome. Genetic testing also revealed a de novo mutation in transforming growth factor beta receptor 2.

MANAGEMENT

Regular cardiovascular surveillance for aneurysms and dissections, and aggressive surgical treatment of vascular disease.

Phenotypic Heterogeneity of Marfan-Like Connective Tissue Disorders Associated With Mutations in the Transforming Growth Factor-.BETA. Receptor Genes

BACKGROUND

Mutations in the genes for transforming growth factor-beta receptor (TGFBR) have been identified in patients with Marfan syndrome (MFS) and Marfan-like connective tissue disorders. There are several syndromes associated with mutations in TGFBR genes, including Loeys-Dietz syndrome (LDS), MFS2, Furlong syndrome, and Shprintzen-Goldberg syndrome. However, with the exception of the first report by Loeys et al, the phenotypic features of patients with TGFBR gene mutations have not been precisely reported.

METHODS AND RESULTS

A total of 18 patients suspected of having MFS were recruited and 7 were diagnosed with MFS and mutations in FBN1. Among the remaining 11 patients, 1 patient had mutations in TGFBR1, 2 had mutations in TGFBR2, and 1 had mutations in COL3A1. The clinical manifestations of the 3 patients with TGFBR gene mutations were examined according to the list of 36 clinical features described in the first report by Loeys et al. The clinical manifestations of these 3 patients differed from those previously observed in patients with MFS2, Furlong syndrome, and Shprintzen-Goldberg syndrome. Thus, the most probable diagnosis of these 3 patients was LDS, despite the fact that they presented with only a fraction of the 36 clinical features associated with LDS.

CONCLUSIONS

Although the number of the patients was limited, the findings support the notion that mutations in the TGFBR gene may be associated with greater phenotypic heterogeneity than previously reported.

Genetic Basis of Thoracic Aortic Aneurysms and Dissections: Potential Relevance to Abdominal Aortic Aneurysms

Ascending thoracic aortic aneurysms leading to type A dissections (TAAD) have long been known to occur in association with a genetic syndrome such as Marfan syndrome (MFS). More recently, TAAD has also been demonstrated to occur as an autosomal dominant disorder in the absence of syndromic features, termed familial TAAD. Familial TAAD demonstrates genetic heterogeneity, and linkage studies have identified TAAD loci at 5q13-14 (TAAD1), 11q23 (FAA1), 3p24-25 (TAAD2), and 16p12.2-13.13. The genetic heterogeneity of TAAD is reflected by variation in disease in terms of the age of onset, progression, penetrance, and association with additional cardiac and vascular features. The underlying genetic heterogeneity of TAAD is reflected in the phenotypic variation associated with familial TAAD with respect to age of onset, progression, penetrance, and association with additional cardiac and vascular features. Mutations in the TGFBR2 gene have been identified as the cause of disease linked to the 3p24-25 locus, implicating dysregulation of TGF-beta signaling in TAAD. Mutations in myosin heavy chain (MYH11), a smooth muscle cell-specific contractile protein, have been identified in familial TAAD associated with patent ductus arteriosus (PDA) linked to 16p12.2-12.13. The identification of these novel disease pathways has led to new directions for future research addressing the pathology and treatment of TAAD.

Recent progress in genetics of Marfan syndrome and Marfan-associated disorders

Marfan syndrome (MFS, OMIM #154700) is a hereditary connective tissue disorder, clinically presenting with cardinal features of skeletal, ocular, and cardiovascular systems. In classical MFS, changes in connective tissue integrity can be explained by defects in fibrillin-1, a major component of extracellular microfibrils. However, some of the clinical manifestations of MFS cannot be explained by mechanical properties alone. Recent studies manipulating mouse Fbn1 have provided new insights into the molecular pathogenesis of MFS. Dysregulation of transforming growth factor beta (TGFbeta) signaling in lung, mitral valve and aortic tissues has been implicated in mouse models of MFS. TGFBR2 and TGFBR1 mutations were identified in a subset of patients with MFS (MFS2, OMIM #154705) and other MFS-related disorders, including Loeys-Dietz syndrome (LDS, #OMIM 609192) and familial thoracic aortic aneurysms and dissections (TAAD2, #OMIM 608987). These data indicate that genetic heterogeneity exists in MFS and its related conditions and that regulation of TGFbeta signaling plays a significant role in these disorders.

Persistent ductus arteriosus in the Brown-Norway inbred rat strain

Persistent ductus arteriosus (PDA) is a common cardiovascular anomaly in children caused by the pathologic persistence of the left sixth pharyngeal arch artery. The inbred Brown-Norway (BN) rat presents with increased vascular fragility due to an aortic elastin deficit resulting from decreased elastin synthesis. The strikingly high prevalence of PDA in BN rats in a pilot study led us to investigate this vascular anomaly in 12 adolescent BN rats. In all BN rats, a PDA was observed macroscopically, whereas a ligamentum arteriosum was found in adult controls. The macroscopic appearance of the PDA was tubular (n = 2), stenotic (n = 8), or diverticular (n = 2). The PDA had the structure of a muscular artery with intimal thickening. In the normal closing ductus of the neonatal controls, the media consisted of layers of smooth muscle cells (SMCs) intermingled with layers of elastin. The intima was thin and poor in elastin. By contrast, the media of PDA in BN rats elastin lamellae were absent and the intima contained many elastic fibers. The abnormal distribution of elastin in the PDA of BN rats suggests that impaired elastin metabolism is related to the persistence of the ductus and implicates a genetically determined factor that may link the PDA with aortic fragility.

Clinical features in a family with an R460H mutation in transforming growth factor beta receptor 2 gene

OBJECTIVES

To describe the clinical findings and natural history in 22 carriers of an R460H mutation in the transforming growth factor beta receptor 2 gene (TGFbetaR2) from a five-generation kindred ascertained by familial aortic dissection.

METHODS

13 of the confirmed carriers were interviewed and examined, and information about the remaining carrier was obtained from medical records. Clinical information about deceased individuals was obtained, when possible, from postmortem reports, death certificates and medical records.

RESULTS

There have been eight sudden deaths; the cause of death was aortic dissection in all six cases in which a postmortem examination was performed. Three individuals had undergone aortic replacement surgery. Dissection had occurred throughout the aorta, and in one case in the absence of aortic root dilatation. Subarachnoid haemorrhage, due to a ruptured berry aneurysm, had occurred in two individuals. Four gene carriers and one deceased family member who were investigated had tortuous cerebral blood vessels. One had tortuous vertebral arteries, two had tortuous carotid arteries and one a tortuous abdominal aorta. Two individuals were found to have a brachiocephalic artery aneurysm and a subclavian artery aneurysm, respectively.

CONCLUSIONS

Despite the predisposition to aortic dilatation and dissection, individuals did not frequently manifest the skeletal features of Marfan syndrome, with the exception of joint hypermobility. No one individual had ocular lens dislocation. Striae and herniae were common. There was some overlap with Ehlers-Danlos syndrome type 4, OMIM 130050, with soft translucent skin, which is easily bruised. Other features were arthralgia, migraine and a tendency to fatigue easily, varicose veins and prominent skin striae. This family provides further evidence that mutations in TGFbetaR2 cause a distinct syndrome that needs to be distinguished from Marfan syndrome to direct investigation and management of patients and shows the natural history, spectrum of clinical features and variable penetrance of this newly recognised condition.

Genetic Analysis of Familial Connective Tissue Alterations Associated With Cervical Artery Dissections Suggests Locus Heterogeneity

Background and Purpose— Cervical artery dissections (CAD) can be associated with connective tissue aberrations in skin biopsies. The analysis of healthy relatives of patients suggested that the connective tissue phenotype is familial with an autosomal dominant inheritance.

Methods— We performed genetic linkage studies in 3 families of patients with CAD. Connective tissue phenotypes for the patients and all family members were assessed by electron microscopic study of skin biopsies. A genome-wide linkage analysis of 1 family (1 patient with 8 healthy relatives) indicated 2 candidate loci. Three genes were subsequently studied by sequence analysis. Part of the genome was also studied by linkage analysis in 2 further families.

Results— The genome-wide scan in a single family suggested linkage between the hypothetical mutation causing the connective tissue phenotype and informative genetic markers on chromosome 15q24 (logarithm of the odds score: Z = +2.1). A second possible candidate locus ( Z =+1.9) was found on chromosome 10q26. Sequence analysis of 3 candidate genes in the suggestive locus (chondroitin sulfate proteoglycan4 [ CSPG4 ], lysyl oxidase-like1 [ LOXL1 ] and fibroblast growth factor receptor2 [ FGFR2 ]) did not lead to the identification of a mutation responsible for connective tissue alterations. In 2 additional smaller families the loci on chromosome 15q24 and 10q26 were excluded by linkage analysis.

Conclusions— Linkage analysis of a large family with CAD-associated connective tissue alterations suggested the presence of a candidate locus on chromosome 15q2 or on chromosome 10q26. Sequence analysis did not lead to the identification of a mutated candidate gene in 1 of these loci. The study of 2 additional pedigrees indicated locus heterogeneity for the connective tissue phenotype of CAD patients.

Two novel and one known mutation of the TGFBR2 gene in Marfan syndrome not associated with FBN1 gene defects

TGF-beta-receptor 2 (TGFBR2) gene defects have been recently associated with Marfan syndrome (MFS) with prominent cardio-skeletal phenotype in patients with negative fibrillin-1 (FBN1) gene screening. Four mutations have been identified to date in five unrelated families. We screened TGFBR2 gene by direct automated sequencing in two adult patients diagnosed with MFS according to Ghent criteria, and in one girl clinically suspected as affected on the basis of a major cardiovascular criterion and skeletal involvement, all proven not to carry mutations in the exon-intron boundaries of FBN1 gene. We identified two novel and one known TGFBR2 gene mutations in the three unrelated probands. The D446N was identified in a 4-year-old girl with de novo disease characterized by severe cardiovascular disease and skeletal involvement. The M425V and R460H mutations were identified in two familial, autosomal dominant MFSs, both characterized by major cardio-skeletal signs and absence of major ocular signs. The mutation R460H has been recently reported in a family with thoracic aortic aneurysms and dissection. The three mutations are absent in 192 controls and affect evolutionarily conserved residues of the serine/threonine kinase domain (exon 5). Our data support the recently reported association between TGFBR2 gene and MFS without major ocular signs (MFS2). The number of genotyped cases however is too low to confirm that major ocular signs are characteristically absent in MFS2. Accordingly, all patients proven or suspected to be affected by MFS with negative FBN1 gene screening could benefit from rapid investigation of the TGFBR2 gene.

The molecular genetics of Marfan syndrome and related disorders

Marfan syndrome (MFS), a relatively common autosomal dominant hereditary disorder of connective tissue with prominent manifestations in the skeletal, ocular, and cardiovascular systems, is caused by mutations in the gene for fibrillin-1 (FBN1). The leading cause of premature death in untreated individuals with MFS is acute aortic dissection, which often follows a period of progressive dilatation of the ascending aorta. Recent research on the molecular physiology of fibrillin and the pathophysiology of MFS and related disorders has changed our understanding of this disorder by demonstrating changes in growth factor signalling and in matrix-cell interactions. The purpose of this review is to provide a comprehensive overview of recent advances in the molecular biology of fibrillin and fibrillin-rich microfibrils. Mutations in FBN1 and other genes found in MFS and related disorders will be discussed, and novel concepts concerning the complex and multiple mechanisms of the pathogenesis of MFS will be explained.

Genetic basis of thoracic aortic aneurysms and aortic dissections

Ascending thoracic aortic aneurysms leading to type A dissections (TAAD) can occur in association with a genetic syndrome, such as Marfan syndrome (MFS), or as an autosomal dominant disorder in the absence of syndromic features, termed familial TAAD. Familial TAAD demonstrates genetic heterogeneity, and linkage studies have identified three TAAD loci at 5q13-14 (TAAD1), 11q23 (FAA1), and 3p24-25 (TAAD2). The underlying genetic heterogeneity of TAAD is reflected in the phenotypic variation associated with familial TAAD with respect to age of onset, progression, penetrance, and association with additional cardiac and vascular features. Recently, mutations in the TGFBR2 gene have been identified as the cause of disease linked to the TAAD2 locus, supporting the hypothesis that dysregulation of TGFbeta signaling is a mechanism leading to aneurysms and dissections. The recent identification of the TGFbeta pathway as a key target in the molecular pathogenesis of TAAD has opened new avenues for future genetic and therapeutic research.

Molecular genetics of Marfan syndrome

PURPOSE OF REVIEW

Marfan syndrome, the founding member of connective tissue disorders, is characterized by involvement of three major systems (skeletal, ocular, and cardiovascular) due to alteration in microfibrils. FBN1 at 15q21.1 was found to cause Marfan syndrome in 1991, and in 2004 TGFBR2 at 3p24.1 was newly identified as the Marfan syndrome type II gene. Several studies implied that fibrillin-1 and transforming growth factor-beta (TGF-beta) signaling are functionally related in extracellular matrix. Identification of TGFBR2 mutations in Marfan syndrome type II provided the direct evidence of the relation in humans.

RECENT FINDINGS

More than 500 FBN1 mutations have been found in Marfan syndrome, tentative genotype - phenotype correlations have emerged, and mouse models are providing insight into pathogenic mechanisms. TGFBR2 mutations are still limited, however, in 2005 were also reported to cause a new aneurysm syndrome. Functional association between fibrillin-1 and TGF-beta signaling in extracellular matrix has been presented.

SUMMARY

This review focuses on recent molecular genetics advances in Marfan syndrome and overlapping connective tissue disorders. Mutation spectrum of FBN1 and TGFBR2 in relation to phenotype is presented. Functional relation between fibrillin-1 and TGF-beta signaling is discussed. Future prospects in the study of Marfan syndrome are presented.

Newly mapped gene for thoracic aortic aneurysm and dissection

Thoracic aortic aneurysm and dissection (TAAD) is associated with high mortality and medical expense. These poor outcomes are preventable by surgical repair; however, identifying at-risk individuals is difficult. Researchers are actively surveying the human genome (the repository of human genes) to characterize the genetic determinants of TAAD by identifying chromosomal regions likely to harbor such predisposing genes. In previous studies, investigators identified genetic markers shared by a subset of families who were ascertained to have the disease, which clustered into 2 chromosomal regions: 5q13-q15 (TAAD1) and 11q23.2-q24 (familial aortic aneurysm [FAA1]). In a subsequent study, a third chromosomal region at 3p24-25 (TAAD2) was found to contribute to TAAD in a 4-generation, 52-member family that displayed little evidence of sharing either the TAAD1 or FAA1 regions. Although additional regions of the genome may contribute to TAAD, investigators are focusing their efforts on identifying the actual genes and the specific mutations that participate in the disease process. The goal of these endeavors is to develop screening tests to identify individuals at risk for familial TAAD. This genetic discovery has significant clinical implications because high-risk individuals and families can be closely monitored and can benefit from preventative surgical repairs.

Genotype-phenotype correlation in congenital heart disease

PURPOSE OF REVIEW

The understanding of the etiology of congenital cardiac lesions is rapidly progressing from the recognition of embryologic origins to insight into the genetic basis for these disorders. Concurrently, in this era, great effort is being expended to gather data that will generate clinically useful genotype-phenotype correlation. This rapidly evolving area of inquiry, in which the clinical implications of mutation status are fully explored, makes available information applicable to those involved in all aspects of congenital cardiac disease.

RECENT FINDINGS

Three syndromes with cardiovascular phenotypes were selected for review. Each has received a great deal of attention in the recent past based on improved understanding of the range of mutations expressed and the relation of these mutations to clinical findings. These three syndromes--Noonan, Marfan, and long QT syndrome--span the range of congenital heart disease and provide examples of genotype-phenotype correlation.

SUMMARY

Better understanding of the clinical implications of specific mutations should allow not only for more sensitive and specific diagnoses to be made but also for improvements in therapeutic options and efficacy.

Comprehensive molecular screening of theFBN1gene favors locus homogeneity of classical Marfan syndrome

In order to estimate the contribution of mutations at the fibrillin-1 locus (FBN1) to classical Marfan syndrome (MFS) and to study possible phenotypic differences between patients with an FBN1 mutation vs. without, a comprehensive molecular study of the FBN1 gene in a cohort of 93 MFS patients fulfilling the clinical diagnosis of MFS according to the Ghent nosology was performed. The initial mutation screening by CSGE/SSCP allowed identification of an FBN1-mutation in 73 patients. Next, sequencing of all FBN1-exons was performed in 11 mutation-negative patients, while in nine others, DHPLC was used. This allowed identification of seven and five additional mutations, respectively. Southern blot analysis revealed an abnormal hybridization pattern in one more patient. A total of 23 out of the 85 mutations identified here are reported for the first time. Phenotypic comparison of MFS patients with cysteine-involving mutations vs. premature termination mutations revealed significant differences in ocular and skeletal involvement. The phenotype of the eight patients without proven FBN1 mutation did not differ from the others with respect to the presence of major cardiac, ocular, and skeletal manifestations or positive familial history. Most likely, a portion of FBN1-mutations remains undetected because of technical limitations. In conclusion, the involvement of the FBN1-gene could be demonstrated in at least 91% of all MFS patients (85/93), which strongly suggests that this gene is the predominant, if not the sole, locus for MFS.

Heterozygous TGFBR2 mutations in Marfan syndrome

Marfan syndrome is an extracellular matrix disorder with cardinal manifestations in the eye, skeleton and cardiovascular systems associated with defects in the gene encoding fibrillin (FBN1) at 15q21.1 (ref. 1). A second type of the disorder (Marfan syndrome type 2; OMIM 154705) is associated with a second locus, MFS2, at 3p25-p24.2 in a large French family (family MS1). Identification of a 3p24.1 chromosomal breakpoint disrupting the gene encoding TGF-beta receptor 2 (TGFBR2) in a Japanese individual with Marfan syndrome led us to consider TGFBR2 as the gene underlying association with Marfan syndrome at the MSF2 locus. The mutation 1524G-->A in TGFBR2 (causing the synonymous amino acid substitution Q508Q) resulted in abnormal splicing and segregated with MFS2 in family MS1. We identified three other missense mutations in four unrelated probands, which led to loss of function of TGF-beta signaling activity on extracellular matrix formation. These results show that heterozygous mutations in TGFBR2, a putative tumor-suppressor gene implicated in several malignancies, are also associated with inherited connective-tissue disorders.