The Marfan syndrome

Left ventricular diastolic dysfunction in children and young adults with Marfan syndrome

Adults with Marfan syndrome (MFS) demonstrate abnormal aortic elastic properties manifest by decreased aortic distensibility and increased aortic stiffness. Left ventricular (LV) diastolic dysfunction has been reported in adults with MFS. The objective of this study was to assess the frequency of LV diastolic dysfunction in a group of children and young adults with MFS and to determine whether diastolic dysfunction is associated with hemodynamic alterations of the aorta. Review of echocardiographic findings in 40 patients with MFS was performed to assess LV size, systolic function, isovolumic relaxation time (IVRT), mitral inflow velocities, deceleration time (DT) of mitral E wave, and aortic root dimension. No patient had significant valvar disease or was on any cardiac medication at the time of study. A group of 40 age and sex-matched healthy subjects undergoing echocardiography served as controls. Significant differences in LV diastolic function were found between MFS patients and controls. MFS patients had prolonged DT and IVRT and decreased mitral E/A ratio, suggesting impaired LV relaxation. No relationship between aortic root dimension and diastolic performance was identified. Left ventricular diastolic dysfunction may be an early marker of myocardial involvement in young MFS patients occurring independently of aortic root dilatation.

Functional analysis of zebrafish microfibril-associated glycoprotein-1 (Magp1) in vivo reveals roles for microfibrils in vascular development and function

Mutations in fibrillin-1 (FBN1) result in Marfan syndrome, demonstrating a critical requirement for microfibrils in vessel structure and function. However, the identity and function of many microfibril-associated molecules essential for vascular development and function have yet to be characterized. In our morpholino-based screen for members of the secretome required for vascular development, we identified a key player in microfibril formation in zebrafish embryogenesis. Microfibril-associated glycoprotein-1 (MAGP1) is a conserved protein found in mammalian and zebrafish microfibrils. Expression of magp1 mRNA is detected in microfibril-producing cells. Analysis of a functional Magp1-mRFP fusion protein reveals localization along the midline and in the vasculature during embryogenesis. Underexpression and overexpression analyses demonstrate that specific Magp1 protein levels are critical for vascular development. Integrin function is compromised in magp1 morphant embryos, suggesting that reduced integrin-matrix interaction is the main mechanism for the vascular defects in magp1 morphants. We further show that Magp1 and fibrillin-1 interact in vivo. This study implicates MAGP1 as a key player in microfibril formation and integrity during development. The essential role for MAGP1 in vascular morphogenesis and function also supports a wide range of clinical applications, including therapeutic targets in vascular disease and cardiovascular tissue engineering.

Fibrillins: from biogenesis of microfibrils to signaling functions

Fibrillins are large proteins that form extracellular microfibril suprastructures ubiquitously found in elastic and nonelastic tissues. Mutations in fibrillin-1 and -2 lead to a number of heritable connective tissue disorders generally termed fibrillinopathies. Clinical symptoms in fibrillinopathies manifest in the skeletal, ocular, and cardiovascular systems and highlight the importance of fibrillins in development and homeostasis of tissues and organs, including blood vessels, bone, and eye. Microfibrils appear to have dual roles in (1) conferring mechanical stability and limited elasticity to tissues, and (2) modulating the activity of growth factors of the transforming growth factor beta (TGF-beta) superfamily. This chapter's focus is on the biogenesis of microfibrils, developmental expression patterns of fibrillins, signaling functions of microfibrils, and mouse models deficient in fibrillins.

Aortic root growth in men and women with the Marfan's syndrome

The leading cause of premature death in patients with Marfan's syndrome (MS) is type A aortic dissection or rupture due to progressive aortic root dilation. The aim of this study was to analyze aortic root growth in 113 men and 108 women with MS. All patients were prospectively followed with serial echocardiograms of the native aortic root. At baseline, women had on average a 5-mm smaller aortic root diameter adjusted for age than men. Average aortic root growth was 0.42 mm/year (SE 0.05) in men and 0.38 mm/year (SE 0.04) in women. On the basis of aortic root growth rates, the men and women could be divided into 2 normally distributed subgroups: fast and slow growers. Approximately 1 in 7 men (1.5 mm/year, SE 0.5) and approximately 1 in 9 women (1.8 mm/year, SE 0.3) had fast-growing aortic root diameters. Significantly more type A dissections (25% vs 4%, p <0.001) were observed in fast growers than in slow growers; this was found in men and women. Type A dissections were observed in 4 men and 9 women. By reducing the cut-off value by 5 mm for elective aortic root replacement in women, type A dissections could have been prevented in 3 women. In conclusion, guidelines should take gender differences into account, and therefore, the investigators propose reducing the threshold for elective aortic root replacement in women with MS by 5 mm.

Growth-reductive therapy in children with marfan syndrome

OBJECTIVES

To determine the accuracy and precision of 2 height-prediction methods in Marfan syndrome and to assess the growth-reductive effect and side effects of sex hormone treatment.

STUDY DESIGN

In a retrospective study in 31 untreated (17 boys) and 43 treated patients (21 boys) with Marfan syndrome, we assessed bone age and predicted adult height by 2 methods. The accuracy of the methods was assessed in the untreated group. The effect of therapy was corrected for outcome in the untreated group and other confounding variables with multivariate analysis.

RESULTS

Accuracy strongly varied with sex, chronological age, and prediction method. Overall precision was low. Treatment was started at a mean age of 12.8 +/- 1.4 years (boys) and 11.4 +/- 1.2 years (girls). With multiple regression analysis, a statistically significant effect was observed only in boys using a pharmacologic dosage (5.5 cm, 95% CI 0.96-10.1 cm; P = .02). Side effects were worsening of acne and weight and muscle gain.

CONCLUSIONS

In adolescents with Marfan syndrome, the accuracy and precision of 2 height-prediction methods were limited. The apparent growth-reductive effect of sex hormone treatment appears similar to earlier reports on adolescents with constitutional tall stature. There were no clinically important short-term side effects.

Sequential deposition of latent TGF-β binding proteins (LTBPs) during formation of the extracellular matrix in human lung fibroblasts

Latent TGF-beta binding proteins (LTBPs) mediate the targeting of latent TGF-beta complexes into ECM structures, which is important for TGF-beta activation and functions. LTBPs-1, -3 and -4 associate with and regulate the bioavailability of TGF-betas. We investigated whether LTBP-3 and -4 are associated with pericellular fibrillar structures of human lung fibroblast ECM, and which of their domains are important for this function. Immunoblotting analyses of isolated insoluble matrices as well as immunofluorescence analyses and confocal microscopy indicated that both LTBP-3 and -4 get assembled into the ECM. Interestingly, LTBP-4 was not detected until 7-10 days of culture and LTBP-3 until 14 days of culture. This was a major difference from the deposition kinetics of LTBP-1, which was detected already within 2 days of culture. Expression analyses by real time RT-PCR indicated that the slow appearance of LTBP-3 and -4 was due to the low expression levels soon after subculture. Recombinant N-terminal fragments of LTBP-3 and -4 bound readily to fibroblast ECM. The C-terminal domain of LTBP-4, but not of LTBP-3, also associated with the matrix structures. The levels of ECM-associated latent complexes of TGF-beta1 increased in parallel with the increased production and deposition of the LTBPs. The amount of active TGF-beta in the conditioned medium decreased during extended culture. Our results suggest that ECM is an important site of deposition also for LTBP-3 and -4 and that the temporal and spatial targeting of the TGF-beta complexes are associated with ECM maturation.

Modification of the Structure and Function of Fibrillin-1 by Homocysteine Suggests a Potential Pathogenetic Mechanism in Homocystinuria

Homocystinuria, a disorder originating in defects in the methionine metabolism, is characterized by an elevated plasma concentration of homocysteine. Most patients have a defect in the cystathionine-beta-synthase, the key enzyme in the conversion of homocysteine to cysteine. Many abnormalities in the connective tissue of patients with homocystinuria resemble those seen in Marfan syndrome, caused by mutations in fibrillin-1. These observations led to the hypothesis that the structure and function of fibrillin-1 is compromised in patients with homocystinuria. To test this hypothesis we produced recombinant human fibrillin-1 fragments spanning the central portion of the molecule (8-Cys/transforming growth factor-beta binding domain 3 to calcium binding EGF domain 22) and extensively analyzed the potential of homocysteine to modify structural and functional properties of these proteins. Circular dichroism spectroscopy revealed moderate changes of their secondary structures after incubation with homocysteine. Equilibrium dialysis demonstrated a number of high affinity calcium binding sites in the tandemly repeated calcium binding epidermal growth factor-like domains 11-22. Calcium binding of homocysteine-modified fragments was completely abolished. Incubation of the recombinant proteins with homocysteine rendered the analyzed calcium binding EGF domains as well as the 8-Cys/transforming growth factor-beta binding domain 3 significantly more susceptible to proteolytic degradation. Furthermore, data were obtained demonstrating that homocysteine can covalently modify fibrillin-1 via disulfide bonds. These data strongly suggest that structural and functional modifications as well as degradation processes of fibrillin-1 in the connective tissues of patients with homocystinuria play a major role in the pathogenesis of this disorder.

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.

Calcification of elastic fibers in human atherosclerotic plaque

The present study was undertaken to systematically investigate whether calcification of elastic fibers occurs in human atherosclerotic plaques. Fourteen carotid artery segments obtained by endarterectomy were examined by a combination of electron microscopy and cytochemistry. The analysis demonstrated that calcification of elastic fibers occurred in all 14 specimens. Two distinct types of calcification of elastic fibers were identified. In type I calcification, elastin itself was observed to undergo calcification and no visible structural alterations preceded the calcification. In type II of calcification, structural alteration of elastin preceded calcification of elastic fibers and included vacuolization of elastin accompanied by the accumulation of neutral lipids and unesterified cholesterol within altered elastic fibers. In type II calcification, calcified deposits were found to form in an association with unesterified cholesterol. Type II calcification was widespread throughout the plaque matrix while type I calcification occurred only in the deep portions of plaques.

Evaluation of left ventricular dimensions and function in Marfan's syndrome without significant valvular regurgitation

Left ventricular dimensions and systolic function were studied using echocardiography in 234 patients with Marfan's syndrome without significant valvular regurgitation. Left ventricular dimensions and systolic function were found to be normal in most patients with Marfan's syndrome. Some involvement of the left ventricle may have been present in a small group of these patients. No patients, however, fulfilled the criteria for dilated cardiomyopathy.

TGF-beta-dependent pathogenesis of mitral valve prolapse in a mouse model of Marfan syndrome

Mitral valve prolapse (MVP) is a common human phenotype, yet little is known about the pathogenesis of this condition. MVP can occur in the context of genetic syndromes, including Marfan syndrome (MFS), an autosomal-dominant connective tissue disorder caused by mutations in fibrillin-1. Fibrillin-1 contributes to the regulated activation of the cytokine TGF-beta, and enhanced signaling is a consequence of fibrillin-1 deficiency. We thus hypothesized that increased TGF-beta signaling may contribute to the multisystem pathogenesis of MFS, including the development of myxomatous changes of the atrioventricular valves. Mitral valves from fibrillin-1-deficient mice exhibited postnatally acquired alterations in architecture that correlated both temporally and spatially with increased cell proliferation, decreased apoptosis, and excess TGF-beta activation and signaling. In addition, TGF-beta antagonism in vivo rescued the valve phenotype, suggesting a cause and effect relationship. Expression analyses identified increased expression of numerous TGF-beta-related genes that regulate cell proliferation and survival and plausibly contribute to myxomatous valve disease. These studies validate a novel, genetically engineered murine model of myxomatous changes of the mitral valve and provide critical insight into the pathogenetic mechanism of such changes in MFS and perhaps more common nonsyndromic variants of mitral valve disease.

Molecular effects of homocysteine on cbEGF domain structure: insights into the pathogenesis of homocystinuria

Homocystinuria is an inborn error of methionine metabolism that results in raised serum levels of the highly reactive thiol-containing amino acid homocysteine. Homocystinurics often exhibit phenotypic abnormalities that are similar to those found in Marfan syndrome (MFS), a heritable connective tissue disorder that is caused by reduced levels of, or defects in, the cysteine-rich extracellular matrix (ECM) protein fibrillin-1. The phenotypic similarities between homocystinuria and MFS suggest that elevated homocysteine levels may result in an altered function of fibrillin-1. We have used recombinant calcium binding epidermal growth factor-like (cbEGF) domain fragments from fibrillin-1, and an unrelated protein Notch1, to analyse the effects of homocysteine on the native disulphide (cystine) bonds of these domains. We show using analytical reverse phase, high performance liquid chromatography (HPLC), electrospray ionisation mass spectrometry (ESI-MS) and limited proteolysis that homocysteine attacks intramolecular disulphide bonds causing reduction of cystine and domain misfolding, and that the effects of homocysteine are dependent on its concentration. We also identify the importance of calcium binding to cbEGF domains for their stabilisation and protection against homocysteine attack. Collectively, these data suggest that reduction of intramolecular cbEGF domain disulphide bonds by homocysteine and the resulting disruption of this domain fold may contribute to the change in connective tissue function seen in homocystinuria. Furthermore, since we show that the effects of homocysteine are not unique to fibrillin-1, other cbEGF-containing proteins may be implicated in the pathogenic mechanisms underlying homocystinuria.

Microfibrils at basement membrane zones interact with perlecan via fibrillin-1

Mutational defects in fibrillin-rich microfibrils give rise to a number of heritable connective tissue disorders, generally termed microfibrillopathies. To understand the pathogenesis of these microfibrillopathies, it is important to elucidate the supramolecular composition of microfibrils and their interaction properties with extracellular matrix components. Here we demonstrate that the proteoglycan perlecan is an associated component of microfibrils typically close to basement membrane zones. Double immunofluorescence studies demonstrate colocalization of fibrillin-1, the major backbone component of microfibrils, with perlecan in fibroblast cultures as well as in dermal and ocular tissues. Double immunogold labeling further confirms colocalization of perlecan to microfibrils in various tissues at the ultrastructural level. Extraction studies revealed that perlecan is not covalently associated with microfibrils. High affinity interactions between fibrillin-1 and perlecan were found by kinetic binding studies with dissociation constants in the low nanomolar range. A detailed mapping study of the interaction epitopes by solid phase binding assays primarily revealed interactions of perlecan domains I and II with a central region of fibrillin-1. Analysis of perlecan null embryos showed less microfibrils at the dermal-epidermal junction as compared with wild-type littermates. The data presented indicate a functional significance for perlecan in anchoring microfibrils to basement membranes and in the biogenesis of microfibrils.

MDCT angiography of pediatric vascular diseases of the abdomen, pelvis, and extremities

Multi-detector-row computed tomography (MDCT) enables rapid, noninvasive, high-resolution, and three-dimensional imaging of pediatric vascular diseases. In this paper, we explore the adaptation of the MDCT angiographic principles to pediatric patients for vascular diseases of the abdomen, pelvis, and extremities. Special emphasis is placed on the practical aspects of how to perform these studies. Optimizations of scan parameters, contrast medium usage, radiation dose, and three-dimensional image processing are discussed in detail. We provide practical guidance on how to choose between MR angiography and CT angiography. Finally, we review important pediatric vascular diseases, categorized into traumatic injuries, inherited vascular diseases, congenital vascular diseases, vasculitides, and surgical planning and assessment. In each category, we discuss how CT angiography can be tailored to maximize its clinical benefits.

Recommendations for physical activity and recreational sports participation for young patients with genetic cardiovascular diseases

A group of relatively uncommon but important genetic cardiovascular diseases (GCVDs) are associated with increased risk for sudden cardiac death during exercise, including hypertrophic cardiomyopathy, long-QT syndrome, Marfan syndrome, and arrhythmogenic right ventricular cardiomyopathy. These conditions, characterized by diverse phenotypic expression and genetic substrates, account for a substantial proportion of unexpected and usually arrhythmia-based fatal events during adolescence and young adulthood. Guidelines are in place governing eligibility and disqualification criteria for competitive athletes with these GCVDs (eg, Bethesda Conference No. 26 and its update as Bethesda Conference No. 36 in 2005). However, similar systematic recommendations for the much larger population of patients with GCVD who are not trained athletes, but nevertheless wish to participate in any of a variety of recreational physical activities and sports, have not been available. The practicing clinician is frequently confronted with the dilemma of designing noncompetitive exercise programs for athletes with GCVD after disqualification from competition, as well as for those patients with such conditions who do not aspire to organized sports. Indeed, many asymptomatic (or mildly symptomatic) patients with GCVD desire a physically active lifestyle with participation in recreational and leisure-time activities to take advantage of the many documented benefits of exercise. However, to date, no reference document has been available for ascertaining which types of physical activity could be regarded as either prudent or inadvisable in these subgroups of patients. Therefore, given this clear and present need, this American Heart Association consensus document was constituted, based largely on the experience and insights of the expert panel, to offer recommendations governing recreational exercise for patients with known GCVDs.

The genetic contribution to congenital heart disease

This article reviews the more recent findings on the genetic basis of congenital cardiovascular disease and highlights the clinical applications of these discoveries.

What is new in the Marfan syndrome?

The Marfan syndrome is an autosomal dominant disorder of connective tissue, caused by mutations in the FBN1 gene on chromosome 15. More than 500 mutations have been identified and almost all are unique to an affected individual or family. Genotype--phenotype correlations in the Marfan syndrome have been complicated by the large number of unique mutations reported, as well as by clinical heterogeneity among individuals with the same mutation. A relatively unknown cardiovascular manifestation of Marfan syndrome is dilatation of the main pulmonary artery. Of 50 patients with Marfan syndrome, MR imaging showed in 74% patients an enlarged pulmonary artery root above the upper limit of normal. Aortic elasticity determined by measurement of local distensibility and flow wave velocity with MR imaging is decreased in non-operated patients with Marfan syndrome. Aortic distensibility of the thoracic descending aorta appeared to be the strongest predictor for descending aortic complications. Over the past 30 years improvement of diagnostic modalities and aggressive medical and surgical therapy, have resulted in considerable improvement of life expectancy of patients with Marfan syndrome. Further studies are needed to investigate the role of modulating genes and genotype--phenotype correlations. Long-term follow-up studies may reveal the prognostic significance of aortic elasticity and may identify patients at risk of aortic complications.

RGD-containing fibrillin-1 fragments upregulate matrix metalloproteinase expression in cell culture: a potential factor in the pathogenesis of the Marfan syndrome

The Marfan syndrome (MFS), a relatively common autosomal dominant disorder of connective tissue, is caused by mutations in the gene for fibrillin-1 (FBN1). Fibrillin-1 is the main component of the 10- to 12-nm microfibrils that together with elastin form elastic fibers found in tissues such as the aortic media. Recently, FBN1 mutations have been shown to increase the susceptibility of fibrillin-1 to proteolysis in vitro, and other findings suggest that up-regulation of matrix metalloproteinases (MMP), as well as fragmentation of microfibrils, could play a role in the pathogenesis of MFS. In the present work, we have investigated the influence of fibrillin-1 fragments on the expression of MMP-1, MMP-2, and MMP-3 in a cell culture system. Cultured human dermal fibroblasts were incubated with several different recombinant fibrillin-1 fragments. The expression level of MMP-1, MMP-2, and MMP-3, was determined by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), and the concentration of the corresponding proteins was estimated by quantitative Western blotting. Our results establish that treatment of cultured human dermal fibroblasts with recombinant fibrillin-1 fragments containing the arginine-glycine-aspartic acid (RGD) integrin-binding motif of fibrillin-1 induces up-regulation of MMP-1 and MMP-3. A similar effect was seen upon stimulation with a synthetic RGD peptide. The expression of MMP-2 was not influenced by treatment. Our results suggest the possibility that fibrillin fragments could themselves have pathogenic effects by leading to up-regulation of MMPs, which in turn may be involved in the progressive breakdown of microfibrils thought to play a role in MFS.

Consequences of Cysteine Mutations in Calcium-binding Epidermal Growth Factor Modules of Fibrillin-1

Mutations in fibrillin-1 lead to Marfan syndrome and some related genetic disorders. Many of the more than 600 mutations currently known in fibrillin-1 eliminate or introduce cysteine residues in epidermal growth factor-like modules. Here we report structural and functional consequences of three selected cysteine mutations (R627C, C750G, and C926R) in fibrillin-1. The mutations have been analyzed by means of recombinant polypeptides produced in mammalian expression systems. The mRNA levels for the mutation constructs were similar to wild-type levels. All three mutated polypeptides were secreted by embryonic kidney cells (293) into the culture medium. Purification was readily feasible for mutants R627C and C750G, but not for C926R, which restricted the availability of this mutant polypeptide to selected analyses. The overall folds of the mutant polypeptides were indistinguishable from the wild-type as judged by the ultrastructural shape, CD analysis, and reactivity with a specific antibody sensitive for intact disulfide bonds. Subtle structural changes caused by R627C and C750G, however, were monitored by proteolysis and heat denaturation experiments. These changes occurred in the vicinity of the mutations either as short range effects (R627C) or both short and long range effects (C750G). Enhanced proteolytic susceptibility was observed for R627C and C750G to a variety of proteases. These results expand and further strengthen the concept that proteolytic degradation of mutated fibrillin-1 might be an important potential mechanism in the pathogenesis of Marfan syndrome and other disorders caused by mutations in fibrillin-1.

Dolichonychia in women with Marfan syndrome

OBJECTIVES

Dolichonychia refers to nails that are elongated and slender. This nail morphology has been described in single case reports of patients with Ehlers-Danlos syndrome, hypohidrotic ectodermal dysplasia, and Marfan syndrome.

METHODS

The length and width of fingernails were measured in patients with Marfan syndrome and in individuals without the syndrome. A fingernail index was calculated for each person. A non-parametric sign test was used to compare the mean fingernail index of patients with Marfan syndrome and control subjects.

RESULTS

The fingernail index ranged from 0.92 to 1.52 in patients with Marfan syndrome and from 0.77 to 1.30 in control individuals. The median fingernail index in women with Marfan syndrome (1.455) was significantly greater than the median fingernail index in women control subjects (1.080) (P = 0.035). Dolichonychia, defined as a fingernail index greater than or equal to 1.30, was present in six of eight (75%) of women with Marfan syndrome as compared with only one of 40 (2.5%) of women control subjects.

CONCLUSIONS

Dolichonychia is a physical finding present in some patients with Marfan syndrome. The detection of long narrow fingernails in women should suggest the possibility of Marfan syndrome.

Endoplasmic reticulum stress induces hyaluronan deposition and leukocyte adhesion

There is mounting evidence that perturbations in endoplasmic reticulum (ER) function play a key role in the pathogenesis of a broad range of diseases. We have examined the ability of ER stress to modulate leukocyte binding to colonic and aortic smooth muscle cells. In vitro, control smooth muscle cells bind few leukocytes, but treatment with compounds that induce ER stress, including tunicamycin, A23187, and thapsigargin, promotes leukocyte binding. Likewise, dextran sulfate, another agent capable of inducing ER stress and promoting inflammation in vivo, strongly induces leukocyte adhesion. The bound leukocytes are released by hyaluronidase treatment, indicating a critical role for hyaluronan-containing structures in mediating leukocyte binding. Affinity histochemistry demonstrated that hyaluronan accumulates and is present in cable-like structures in the treated, but not the untreated, cultures and that these structures serve as attachment sites for leukocytes. Hyaluronan-rich regions of both murine and human inflamed colon contain numerous cells that stain intensely for ER-resident chaperones containing the KDEL sequence, demonstrating a relationship between ER stress and hyaluronan deposition in vivo. These results indicate that ER stress may contribute to chronic inflammation by forming a hyaluronan-rich extracellular matrix that is conducive to leukocyte binding.

Molecular pathogenesis of subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH) results from leakage of blood into the subarachnoid space and carries high morbidity and mortality. However, there is limited understanding to date, of the risk factors, cellular, intermediate biochemical and genetic traits predisposing to SAH. Nevertheless, in conjunction with improved methods of diagnostic imaging and less invasive approaches to preventing aneurysmal rupture, there may be utility in gaining a better understanding of the pathogenesis and in identifying pre-disease markers. Additionally, it is not impossible that drugs of value (e.g. matrix or endothelial modifiers) could become available. Several different clinical subtypes can be recognised, distinguished by arterial or venous involvement, presence of unruptured arterial aneurysms, and apparently "sporadic" and "familial" occurrences. Epidemiological risk factors include alcohol consumption and smoking: hypertension is a risk factor for rupture. About 10% seem to reflect strong family history and this subset may be particularly illuminating with respect to the molecular pathogenesis. Haemodynamic stress and poor vascular structure may be the main mechanisms of pathogenesis. The epidemiological and statistical evidence for familial megaphenic genes and modifier genes is reviewed. This review focuses on the pathogenesis, as opposed to inflammatory response to SAH. It sets in context the roles of specific genes and their protein products, such as polycystin (PKD1), fibrillin (FBN1), collagen III (COL3A1), elastin (ELN), collagen IV, protease inhibitor or alpha1-antitrypsin (PI) and proteases. These considerations illustrate the shortfalls in current knowledge, the needs of future biochemical and cellular research and their potential implications for future prevention of this often fatal condition.

Saltatory control of isometric growth in the zebrafish caudal fin is disrupted in long fin and rapunzel mutants

Zebrafish fins grow by sequentially adding new segments of bone to the distal end of each fin ray. In wild type zebrafish, segment addition is regulated such that an isometric relationship is maintained between fin length and body length over the lifespan of the growing fish. Using a novel, surrogate marker for fin growth in conjunction with cell proliferation assays, we demonstrate here that segment addition is not continuous, but rather proceeds by saltation. Saltation is a fundamental growth mechanism shared by disparate vertebrates, including humans. We further demonstrate that segment addition proceeds in conjunction with cyclic bursts of cell proliferation in the distal fin ray mesenchyme. In contrast, cells in the distal fin epidermis proliferate at a constant rate throughout the fin ray growth cycle. Finally, we show that two separate fin overgrowth mutants, long fin and rapunzel, bypass the stasis phase of the fin ray growth cycle to develop asymmetrical and symmetrical fin overgrowth, respectively.

Muscle fibrillin deficiency in Marfan's syndrome myopathy

OBJECTIVE

To report a family with Marfan's syndrome in whom a myopathy was associated with respiratory failure; muscle biopsies from affected individuals were examined to determine whether there were abnormalities in fibrillin.

METHODS

21 family members underwent detailed clinical examination, including neurological and pulmonary assessment. Muscle biopsies in the most severely affected cases were immunostained using monoclonal antibodies to specific fibrillin components. Genomic DNA from all 21 members was analysed for mutations in the fibrillin gene, FBN1, on 15q21.

RESULTS

13 individuals had a C4621T base change in exon 37 of the FBN1 gene, which in four cases segregated with muscle weakness or evidence of respiratory muscle dysfunction or both. Their muscle biopsies revealed an abnormality in fibrillin immunoreactivity.

CONCLUSIONS

Abnormalities in fibrillin can be detected in muscle biopsies from patients with Marfan's syndrome who have myopathy. This pedigree, with a point mutation in FBN1, also draws attention to the potential for respiratory failure associated with myopathy.

Magnetic resonance microscopy quantifies the disease progression in Marfan syndrome mice

PURPOSE

To use noninvasive magnetic resonance microscopy (MRM) to examine aneurysmal disease in the mouse model of Marfan syndrome (MFS).

MATERIALS AND METHODS

A total of eight wild-type (WT) and MFS mice were imaged using MRM; four of them at three different time points over an 8-week period and the remaining animals were imaged at one time point. The maximal cross-sectional area of the aorta was measured by manual tracing and by automated means from combined cardiac and respiratory-gated bright-blood images. Relationships between aortic size and age and the differences between WT and mutant mice aortic size were established.

RESULTS

Maximal cross-sectional aortic areas differed significantly (P < 0.05) between WT and mutant mice for all time points, with MFS mice having larger aortic size. There was a positive correlation between aortic size and age in MFS mice (r = 0.80) with a significant increase from the 14th to the 22nd week (P < 0.05).

CONCLUSION

MRM detected the differences in aortic size between WT and mutant mice over time, demonstrating a potential for noninvasive technique for the assessment of potential therapies in MFS mice.

Fibrillin-1 and fibrillin-2 in human embryonic and early fetal development

The extracellular glycoproteins fibrillin-1 and fibrillin-2 are major components of connective tissue microfibrils. Mutations in the fibrillin-1 and fibrillin-2 genes are responsible for the phenotypical manifestations of Marfan syndrome and congenital contractural arachnodactyly respectively, which emphasizes their essential roles in developmental processes of various tissues. Consistent with this last notion, organ culture experiments have indirectly suggested morphogenic roles for fibrillins in lung and kidney development. In order to contribute to the understanding of the roles of fibrillins in developmental and morphogenetic events, we have investigated the distribution of fibrillin-1 and fibrillin-2 in human embryonic and early fetal tissues between the 5th and the 12th gestational week, i.e. at the beginning of organogenesis. Fibrillin-1 and fibrillin-2 were localized immunohistochemically using specific monoclonal antibodies, mAb 69 and mAb 48, respectively. Both fibrillins are widely distributed in various human anlagen, from early developmental stages. In most embryonic and early fetal human organs such as skin, lung, heart, aorta, central nervous system anlage, nerves, and ganglia, fibrillin-1 and fibrillin-2 follow the same temporo-spatial pattern of distribution. However, in other organs such as kidney, liver, rib anlagen, notochord fibrillin-1 and fibrillin-2 are distributed differentially. The present paper is focused on this aspect. These results suggest different roles for fibrillin-1 and -2 in the development of these structures.

Psychiatric symptoms and Marfan: part of the syndrome or incidental to it?

The authors report the case of a patient who consulted primarily for depression and anxiety and was secondly diagnosed with Marfan syndrome. The question of whether psychiatric symptoms are part of the Marfan syndrome or merely incidental to it is raised.

Mutations of FBN1 and genotype-phenotype correlations in Marfan syndrome and related fibrillinopathies

The Marfan syndrome (MFS) is a pleiotropic, autosomal dominant disorder of connective tissue with highly variable clinical manifestations including aortic dilatation and dissection, ectopia lentis, and a series of skeletal anomalies. Mutations in the gene for fibrillin-1 (FBN1) cause MFS, and at least 337 mainly unique mutations have been published to date. FBN1 mutations have been found not only in MFS but also in a range of connective tissue disorders collectively termed fibrillinopathies ranging from mild phenotypes, such as isolated ectopia lentis, to severe disorders including neonatal MFS, which generally leads to death within the first two years of life. The present article intends to provide an overview of mutations found in MFS and related disorders and to discuss potential genotype-phenotype correlations in MFS.

Diastolic subclinical primary alterations in Marfan syndrome and Marfan-related disorders

BACKGROUND

The extracellular matrix tissue of the myocardium importantly contributes to left ventricular (LV) performance. Inherited connective tissue disorders related to the FBN1 gene could involve cardiac interstitium resulting in functional abnormalities.

HYPOTHESIS

To disclose a primary involvement of myocardium, LV function was studied in 28 patients affected by Marfan syndrome or Marfan-related disorders: 20 Marfan and 8 MASS (Mitral valve prolapse, Myopia, Aortic dilatation, Skeletal involvement, Skin striae) and in 28 healthy, age and gender-matched controls. No valvular regurgitation or any other cardiac alterations were present.

METHODS

Echocardiographic study was performed to investigate LV systolic and diastolic function.

RESULTS

No statistically significant differences were observed between patients and the control group in LV dimensions, systolic function parameters (ejection and shortening fraction), and some diastolic function parameters (E peak, A peak, E/A), while statistically significant differences were found between patients and the control group in LV mass (128.7 +/- 46.6 vs. 83.7 +/- 14.5 g/m2, p<0.008), in isovolumic relaxation time (102.0 +/- 24.0 vs. 80.1 +/- 11.2 ms, p<0.016), and in deceleration time of the E wave (127.5 +/- 19.3 vs. 208.6 +/- 24.5 ms, p<0.001) and the A wave (66.4 +/- 8.2 vs. 87.5 +/- 23.4 ms, p <0.008).

CONCLUSIONS

These data show an unusual pattern of transmitral diastolic flow in which a decreased ventricular compliance and reduced myocardial relaxation coexist. Thus, in Marfan syndrome and in Marfan-related disorders, subclinical diastolic alterations are present independent of valvular disease and might represent an early marker of primary myocardial involvement.

TGGE screening of the entire FBN1 coding sequence in 126 individuals with marfan syndrome and related fibrillinopathies

Mutations in the gene for fibrillin-1 (FBN1) cause Marfan syndrome (MFS), an autosomal dominant heritable disorder of connective tissue with prominent manifestations in the skeletal, ocular, and cardiovascular system. FBN1 mutations have also been identified in a series of related disorders of connective tissue collectively termed type-1 fibrillinopathies. We have developed temperature-gradient gel electrophoresis (TGGE) assays for all 65 FBN1 exons, screened 126 individuals with MFS, other type-1 fibrillinopathies, and other potentially related disorders of connective tissue for FBN1 mutations, and identified a total of 53 mutations, of which 33 are described here for the first time. Several mutations were identified in individuals with fibrillinopathies other than classic Marfan syndrome, including aneurysm of the ascending aorta with only minor skeletal anomalies, and several individuals with only skeletal and ocular involvement. The mutation detection rate in this study was 42% overall, but was only 12% in individuals not fulfilling the diagnostic criteria for MFS, suggesting that clinical overdiagnosis is one reason for the low detection rate observed for FBN1 mutation analysis.

Cardiac risk factors and participation guidelines for youth sports

Accurate assessment of the cardiac system in pediatric and adolescent youth is important. The hemodynamic demands associated with exercise, training, and sport participation are usually positive and beneficial; however, when an underlying cardiac problem exists, it is imperative that such cardiac problems be identified. Safe sport-related cardiac participation guidelines should be provided for young athletes and their families and coaches. This chapter provides a physician perspective on the recognition and current cardiac management considerations for young athletes participating in both static and dynamic types of sports. The most recent guidelines for hypertension in youth are also provided.

Premature termination mutations in FBN1: distinct effects on differential allelic expression and on protein and clinical phenotypes

Marfan syndrome (MFS) and other type 1 fibrillinopathies result from mutations in the FBN1 gene, which encodes the connective-tissue microfibrillar protein fibrillin 1. Attempts at correlating genotype with phenotype have suggested considerable heterogeneity. To define the subtype of fibrillinopathy caused by premature termination codon (PTC) mutations, we integrate genotype information and mRNA expression levels with clinical and biochemical phenotypes. By screening the entire FBN1 gene for mutations, we identified 34 probands with PTC mutations. With the exception of two recurrent mutations, these nonsense and frameshift mutations are unique and span the entire FBN1 gene, from IVS2 to IVS63. Allele-specific reverse-transcriptase polymerase chain reaction analyses revealed differential allelic expression in all studied samples, with variable reduction of the mutant transcript. Fibrillin protein synthesis and deposition into the extracellular matrix were studied by pulse-chase analysis of cultured fibroblasts. In the majority of PTC samples, synthesis of normal-sized fibrillin protein was approximately 50% of control levels, but matrix deposition was disproportionately decreased. Probands and mutation-positive relatives were clinically evaluated by means of a standardized protocol. Only 71% (22/31) of probands and 58% (14/24) of the mutation-positive family members met current clinical diagnostic criteria for MFS. When compared with our previously reported study group of 44 individuals with FBN1 cysteine substitutions, the PTC group showed statistically significant differences in the frequency of individual signs, especially in the ocular manifestations. Whereas large-joint hypermobility was more common, lens dislocation and retinal detachment were distinctly less common in the PTC group. We conclude that PTC mutations have a major impact on the pathogenesis of type 1 fibrillinopathies and convey a distinct biochemical, clinical, and prognostic profile.

Familial abdominal aortic aneurysm: a systematic review of a genetic background

BACKGROUND

Familial clustering of the abdominal aortic aneurysm (AAA) is clear, 12-19% of AAA patients have one or more first-degree relatives with an aneurysm and 4-19% is detected with ultrasound screening.

OBJECTIVES

To review the genetic background of AAA. DESIGN, METHODS AND MATERIALS: Computer searches of the MEDLINE, EMBASE, SUMsearch database and the Cochrane Library and searched reference lists of English language articles concerning the genetics of AAA, candidate gene approach and linkage analysis.

RESULTS

Brothers of AAA patients are at high risk to develop an AAA. The candidate gene approach was performed to detect defects in one of the components of the connective tissue, i.e. type I and III collagen, elastin and fibrillin, the inflammatory cell-derived matrix metalloproteinase, there inhibitors, auto-immune components and components related to atherosclerosis.

CONCLUSION

These studies give us insight in the pathology but do not lead to the specific genetic factor(s) responsible for (familial) AAA. Considering the supposed autosomal dominant inheritance, a gene mutation in one of the structural proteins of the connective tissue is expected. In the future, linkage analysis may resolve the genetic background of AAA.

A nonsense mutation in the fibrillin-1 gene of a Marfan syndrome patient induces NMD and disrupts an exonic splicing enhancer

A nonsense mutation in the fibrillin-1 (FBN1) gene of a Marfan syndrome (MFS) patient induces in-frame exon skipping of FBN1 exon 51. We present evidence, based on both in vivo and in vitro experiments, that the skipping of this exon is due to the disruption of an SC35-dependent splicing enhancer within exon 51. In addition, this nonsense mutation induces nonsense-mediated decay (NMD), which degrades the normally spliced mRNA in the patient's cells. In contrast to NMD, skipping of FBN1 exon 51 does not require translation.

Sudden adult death: a medico-legal series of 77 cases between 1995 and 2000

Among all the autopsies performed between 1995 and 2000 in our Department, 77 adult cases of sudden death were selected. Sex, age, place of death, circumstances of death, causes of death and heart weight were reported from these 77 post-mortem records. A complete forensic autopsy was performed in every case. Sudden death occurred more frequently in males at rest. Strenuous activity was rarely involved in sudden death and 72.7% of the cases died from cardiovascular disease, mainly coronary atherosclerosis. Non-cardiac causes were dominated by pulmonary and neurological diseases. Cardiomegaly was a frequent finding in cases who died from cardiac pathology. This study underlines the importance of complete medico-legal investigations in case of sudden death. Multiple heart samples are required in order to detect focal microscopic lesions, such as myocarditis and some forms of cardiomyopathy with minimal gross abnormalities. The post-mortem diagnosis of such cardiomyopathies is very important because the family of the deceased may undergo a possible screening. Toxicology is useful in the diagnosis of epileptic seizure and in identifying drugs like metamphetamine as a risk factor for some lethal cardiovascular pathologies such as aortic dissection. Molecular biology can also be helpful when limits of morphological diagnosis have been reached.

Evaluation and application of denaturing HPLC for mutation detection in Marfan syndrome: Identification of 20 novel mutations and two novel polymorphisms in the FBN1 gene

Mutations in the human fibrillin 1 gene (FBN1) cause the Marfan syndrome (MFS), an autosomal dominant connective tissue disorder. Knowledge about FBN1 mutations is important for early diagnosis, management, and genetic counseling. However, mutation detection in FBN1 is a challenge because the gene is very large in size ( approximately 200 kb) and the approximately 350 mutations detected so far are scattered over 65 exons. Conventional methods for large-scale detection of mutations are expensive, technically demanding, or time consuming. Recently, a high-capacity low-cost mutation detection method was introduced based on denaturing high-performance liquid chromatography (DHPLC). To assess the sensitivity and specificity of this method, we blindly screened 64 DNA samples of known FBN1 genotype exon-by-exon using exon-specific DHPLC conditions. Analysis of 682 PCR amplicons correctly identified 62 out of 64 known sequence variants. In three MFS patients of unknown FBN1 genotype, we detected two mutations and eight polymorphisms. Overall, 20 mutations and two polymorphisms are described here for the first time. Our results demonstrate 1) that DHPLC is a highly sensitive (89-99%, P = 0.05) method for FBN1 mutation detection; but 2) that chromatograms with moderate and weak pattern abnormalities also show false positive signals (in all 45-59%, P = 0.05); 3) that the difference in the chromatograms of heterozygous and homozygous amplicons is mostly independent of the type of sequence change; and 4) that DHPLC column conditions, additional base changes, and the amounts of injected PCR products influence significantly the shape of chromatograms. A strategy for FBN1 mutation screening is discussed.

Relationship between craniofacial abnormalities and sleep-disordered breathing in Marfan's syndrome

OBJECTIVES

To examine the prevalence and nature of craniofacial abnormalities in patients with Marfan's syndrome and to investigate the relationship between craniofacial abnormalities and obstructive sleep apnea (OSA) severity in these patients.

DESIGN

Cross-sectional.

SETTING

Marfan's syndrome clinic in a tertiary teaching hospital.

PATIENTS

Fifteen consecutive adult patients (7 men and 8 women; mean [+/- SD] age, 34.8 +/- 13.2 years) who had Marfan's syndrome.

MEASUREMENTS AND RESULTS

Apneic status was determined from standard overnight polysomnography testing. Measurements from standardized lateral cephalometric radiographs were compared to normative data. Thirteen patients had OSA, which was defined as an apnea/hypopnea index (AHI) of > 5 episodes per hour (mean AHI, 22 +/- 15 episodes per hour). A high prevalence of craniofacial abnormalities was found with significant gender differences for some of the variables. Significant abnormalities for the entire group were bimaxillary retrusion, a reduced maxillary length, an increased total anterior face height, a long lower anterior face height, an obtuse gonial angle, a steep mandibular plane, a reduced posterior nasal airway height, a reduced posterior airway space, and an increased distance from the mandibular plane to the hyoid bone. Univariate analysis revealed significant correlations among the total anterior face height, the upper anterior and posterior face heights, the mandibular length, and AHI. There was a significant correlation between the rank of the number of cephalometric abnormalities per patient and AHI in those patients with OSA.

CONCLUSIONS

Craniofacial abnormalities are common in patients with Marfan's syndrome. The relationship between some cephalometric parameters and apnea severity suggests a potential role of craniofacial structure in the pathogenesis of OSA in these patients.

Multi-exon deletions of the FBN1 gene in Marfan syndrome

BACKGROUND

Mutations in the fibrillin -1 gene (FBN1) cause Marfan syndrome (MFS), an autosomal dominant multi-system connective tissue disorder. The 200 different mutations reported in the 235 kb, 65 exon-containing gene include only one family with a genomic multi-exon deletion.

METHODS

We used long-range RT-PCR for mutation detection and long-range genomic PCR and DNA sequencing for identification of deletion breakpoints, allele-specific transcript analyses to determine stability of the mutant RNA, and pulse-chase studies to quantitate fibrillin synthesis and extracellular matrix deposition in cultured fibroblasts. Southern blots of genomic DNA were probed with three overlapping fragments covering the FBN1 coding exons

RESULTS

Two novel multi-exon FBN1 deletions were discovered. Identical nucleotide pentamers were found at or near the intronic breakpoints. In a Case with classic MFS, an in-frame deletion of exons 42 and 43 removed the C-terminal 24 amino acids of the 5th LTBP (8-cysteine) domain and the adjacent 25th calcium-binding EGF-like (6-cysteine) domain. The mutant mRNA was stable, but fibrillin synthesis and matrix deposition were significantly reduced. A Case with severe childhood-onset MFS has a de novo deletion of exons 44-46 that removed three EGF-like domains. Fibrillin protein synthesis was normal, but matrix deposition was strikingly reduced. No genomic rearrangements were detected by Southern analysis of 18 unrelated MFS samples negative for FBN1 mutation screening.

CONCLUSIONS

Two novel deletion cases expand knowledge of mutational mechanisms and genotype/phenotype correlations of fibrillinopathies. Deletions or mutations affecting an LTBP domain may result in unstable mutant protein cleavage products that interfere with microfibril assembly.

Interactions of fibrillin-1 with heparin/heparan sulfate, implications for microfibrillar assembly

Fibrillin-1 is a major constituent of the 10-12 nm extracellular microfibrils. Here we identify, characterize, and localize heparin/heparan sulfate-binding sites in fibrillin-1 and report on the role of such glycosaminoglycans in the assembly of fibrillin-1. By using different binding assays, we localize two calcium-independent heparin-binding sites to the N-terminal (Arg(45)-Thr(450)) and C-terminal (Asp(1528)-Arg(2731)) domains of fibrillin-1. A calcium-dependent-binding site was localized to the central (Asp(1028)-Thr(1486)) region of fibrillin-1. Heparin binding to these sites can be inhibited by a highly sulfated and iduronated form of heparan sulfate but not by chondroitin 4-sulfate, chondroitin 6-sulfate, and dermatan sulfate, demonstrating that the heparin binding regions represent binding domains for heparan sulfate. When heparin or heparan sulfate was added to cultures of skin fibroblasts, the assembly of fibrillin-1 into a microfibrillar network was significantly reduced. Western blot analysis demonstrated that this effect was not due to a reduced amount of fibrillin-1 secreted into the culture medium. Inhibition of the attachment of glycosaminoglycans to core proteins of proteoglycans by beta-d-xylosides resulted in a significant reduction of the fibrillin-1 network. These studies suggest that binding of fibrillin-1 to proteoglycan-associated heparan sulfate chains is an important step in the assembly of microfibrils.

Quantitative assessment of dural ectasia as a marker for Marfan syndrome

PURPOSE

To establish normal values for lumbosacral dural sac dimensions with magnetic resonance (MR) imaging and to use these values to assess the sensitivity and specificity of dural ectasia as a marker for Marfan syndrome.

MATERIALS AND METHODS

MR imaging was performed to measure dural sac diameter (DSD) from L1 through S1 in 44 adult patients with Marfan syndrome and in 44 matched control subjects. DSD values were corrected for vertebral body size, yielding dural sac ratios (DSRs). The control subjects served to establish the upper limit of normal DSR values at the L1 through S1 levels.

RESULTS

Cutoff values for normal DSRs for L1 through S1 were 0.64, 0.55, 0.47, 0.48, 0.48, and 0.57. Significant DSR differences were shown at all levels between patients with Marfan syndrome and control subjects (P <.001 at all levels). At L1 through S1, the sensitivity of dural ectasia as a marker for Marfan syndrome was 45%-77%, and the specificity was 95% or greater. By combining levels L3 and S1, dural ectasia as a marker for Marfan syndrome yielded a sensitivity of 95% (42 of 44 patients) and a specificity of 98% (43 of 44). The presence of dural ectasia excelled, compared with the presence of other Marfan syndrome manifestations in the patient population.

CONCLUSION

Abnormal DSR values at L3 or S1 can be used to identify Marfan syndrome with 95% sensitivity and 98% specificity.

Sports and marfan syndrome: awareness and early diagnosis can prevent sudden death

Marfan syndrome is an autosomal dominant disorder of the connective tissues. Its major manifestations are in the cardiovascular, musculoskeletal, and ocular systems. Recognizing the phenotypic presentation of tall stature, long limbs and fingers, chest deformity, myopia, midsystolic click, and systolic or diastolic murmur can lead to early diagnosis. Morbidity and mortality are primarily caused by cardiovascular involvement. The goal of medical therapy is to retard the aortic root dilation that leads to sudden death from dissection or rupture. Surgical interventions for mitral valve regurgitation and resection of aortic aneurysms are highly effective. In addition, individuals with Marfan syndrome should be restricted from participation in certain sports.