For Fibrillin-1 Research Articles

Abstract 288: Development Of A Phenotypic Screen With 56 Marfan Syndrome Patient-derived Fibroblasts

Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in the extracellular matrix gene coding for fibrillin-1 (FBN1). MFS leads to aortic aneurysms as key feature. Due to the high genetic diversity within the MFS patient population, genotype-phenotype predictions on disease progression and response to therapy remain challenging. Furthermore, current preclinical murine models represent only a subset of FBN1 mutations, which limits translational studies. In this study, we developed a preclinical model using primary cells of MFS patients that represent genetic and clinical variability in order to develop improved drug strategies. Human primary fibroblasts were isolated from skin biopsies derived from MFS patients (n=56) participating in the COMPARE trial. Human aortic smooth muscle cells (AoSMCs) were isolated from aortic tissue derived from MFS patients undergoing prophylactic aortic surgery (n=4). Long-term cultures in 384-well plates were assessed for the extracellular matrix and disease associated pathways. Analysis of all MFS fibroblasts showed either a reduced or abolished fibrillin-1 extracellular matrix network. Moreover, substantially reduced secretion of fibrillin-1 and asprosin in the culture medium was measured, as compared to healthy control fibroblasts. MFS fibroblasts with an abolished fibrillin-1 matrix were associated with patients with more rapid aortic root diameter growth. Exploring disease-relevant pathways revealed reduced nuclear localization of transcription factor KLF4 in MFS fibroblasts, which associated with the level of fibrillin-1 matrix. As a marker for myofibroblasts, α-smooth muscle actin (ASMA) staining was increased in these MFS fibroblasts. These findings were validated in AoSMC cultures, showing similar MFS fibrillin-1 matrix, nuclear KLF4, and ASMA expression profiles. In conclusion, phenotypic screening of patient-derived cells contributes to improved understanding of disease development and is valuable as preclinical tool for risk assessment and drug development for MFS and related conditions.

Effect of the General Inhibitor of Nitric Oxide Synthase (L‐NAME) On Cardiac and Aortic Function and Structure in A Mouse Model of Marfan Syndrome‐Associated Aortic Aneurysm

Marfan Syndrome (MFS) is an autosomal‐dominant connective tissue disorder caused by missense mutations in the gene that encodes for Fibrillin‐1 (FBN1). FBN1 is an extracellular matrix glycoprotein that functions as a scaffolding protein during the formation and maturation of elastic fibers. The mechanism underlying MFS pathogenesis stems from a crosstalk between the Angiotensin‐II pathway and over activation of transforming growth factor‐beta signaling. There are several clinical manifestations seen in MFS, but the most serious and life‐threatening is the aortic aneurysm due to degradation and fragmentation of aortic wall elastin fibers. If left untreated, aortic aneurysm progression may lead to dissection and rupture.Previous studies in the MFS mouse model have shown that the progression of aortic aneurysm is associated with a significant decline in endothelial function and nitric oxide (NO) production in the aortic wall, and that overexpression of endothelial nitric oxide synthase (eNOS) could delay the progression of aortic root aneurysm in MFS mice. A recent study in our lab has also shown that mild aerobic exercise can block aortic aneurysm in MFS mice. It is well established that exercise can improve endothelial function mainly through an increase in eNOS‐mediated NO production. Therefore, we tested the hypothesis that mild aerobic exercise prevents aortic aneurysm progression in the mouse model of MFS mainly through increasing the production of NO within the aortic wall.To test this hypothesis, C57BL/6 WT and MFS mice were subjected to daily treadmill exercise (at 55% of VO2max, starting at 4 weeks of age) in the absence or presence of the general inhibitor of NO production, N(G)‐Nitro‐L‐arginine methyl ester (L‐NAME) at 0.05 g per 100 mL of drinking water. At 6‐months of age, in vivo imaging of the aortic root diameter and pulse wave velocity (PWV) as an index of wall stiffness, was performed using a high‐resolution Vevo2100 ultrasound system. The aortic root diameter at the sinus of Valsalva, and pulse wave velocity were both increased in MFS mice compared to WT, however MFS mice subjected to treadmill exercise had significantly decreased aortic root diameter and pulse wave velocity compared to sedentary MFS mice. In situ analysis of aortic wall integrity was analyzed at 6 months by Van Geison staining. Our results revealed that MFS mice had an increase in elastin fragment count and a decrease in elastin fiber length compared to WT. Interestingly, MFS mice subjected to exercise had fewer elastin fragment count and an increase in elastin fiber length compared to sedentary MFS mice. Interestingly, L‐NAME treatment reversed the protective effects of exercise on aortic root diameter and pulse wave velocity in MFS mice to a level that was not different than MFS sedentary groups. This study provides preliminary evidence that mild aerobic exercise blocks the progression of aortic root dilation in MFS mice through increasing the production of NO within the aortic wall, and further emphasizes the value of increased physical activity in aneurysm population.

Abstract 15530: Single-cell Analysis in Aortic Aneurysmal Tissue From Patients With Marfan Syndrome Reveals Increased Tgf-beta Production but Downregulation of Downstream Canonical Tgf-beta Signaling Pathways

Background: Marfan syndrome (MFS) is caused by mutations in the gene for fibrillin-1 ( FBN1 ); however, the mechanisms by which these mutations cause aortic aneurysms are poorly understood. Although it was hypothesized previously that dysregulation of the complex TGF-β signaling pathway leads to aortic aneurysm formation, FBN1 mutations appear to have a paradoxical effect on TGF-β signaling in MFS. In this study, we evaluated cell-specific TGF-β expression in non-immune cells in MFS aortic tissue. Methods: We performed single-cell RNA sequencing of ascending aortic aneurysm tissues from MFS patients (n=3) undergoing aneurysm repair and age-matched, non-aneurysmal control tissue from cardiac transplant donors and recipients (n=4). Non-immune cells were separated out from the data and analyzed using the Seurat package in R. Differentially expressed genes were identified using edgeR. Results: Conserved gene expression was used to identify populations of smooth muscle cells (SMCs; n=6), fibroblasts (n=3), and endothelial cells (ECs; n=3). We found that TGFB1 was significantly upregulated in quiescent fibroblasts (identified by increased expression of DCN , LUM , and complement factors) with log2FC of 1.30 and FDR 8.25x10 -8 , as well as in activated fibroblasts (identified by increased expression of genes involved in blood vessel repair and healing including ACTA2 , NOTCH3 , THBS2 , and PDGFRB ) with log2FC of 1.25 and FDR 6.15x10 -22 . Despite this increase in TGFB1 , expression of TGF-β receptor genes (predominately TGFBR2 ) as well as downstream SMAD genes was downregulated significantly in the SMC, fibroblast, and endothelial cell clusters. Finally, genes involved in the non-canonical TGF-β pathway, including ERK , JNK, and p38, were not differentially expressed in non-immune cells in MFS compared with control tissues. Conclusion: Increased expression of TGFB1 in non-immune cells in MFS was driven by two clusters of fibroblasts. Despite this, our data do not support associated upregulation of other genes in the canonical or non-canonical TGF-β pathways and in fact support downregulation of canonical TGF-β signaling in non-immune cells of aneurysmal tissues from MFS patients with advanced aortic disease.

Are Fibrillin‐Notch Interactions Important in Development and Disease?

In humans, mutations in the gene for fibrillin‐1 (FBN1) cause both the Marfan syndrome as well as several types of acromelic dysplasias. Musculoskeletal features of the Marfan syndrome (long bone overgrowth and arachnodactyly, joint hypermobility, and a muscle wasting phenotype) are the opposite of those in acromelic dysplasias (short stature and brachydactyly, joint stiffness, and a hypermuscular build). How mutations in the same gene can result in opposite phenotypes is poorly understood. Mutations in FBN2 cause congenital contractural arachnodactyly, which features a mixture of related musculoskeletal features (muscle hypoplasia, contractures of the large and small joints and arachnodactyly).The fibrillins are multifunctional glycoproteins that polymerize into extracellular matrix microfibrils. Although we have associated fibrillin microfibril structure with the opposite musculoskeletal features of Marfan syndrome and acromelic dysplasias, we can only speculate that perturbations in growth factor signaling are involved. To begin to address this gap in our understanding, we hypothesize that direct interactions between fibrillin and cells coordinate growth factor signaling. Therefore, we searched for interactions between fibrillin and cellular receptors.Fibrillins, like Notch receptors and Notch ligands, are composed of multiple tandemly repeated cbEGF‐like domains. Each fibrillin contains 43 cbEGF‐like domains. What if Notch receptors or ligands also bind to fibrillins in the extracellular matrix? Our biochemical data imply that fibrillin interactions with Notch receptors or ligands are just as likely to occur in vivo as interactions between Notch receptors and known Notch transmembrane ligands. Human genetic evidence support significant roles for Notch signaling components in vascular and musculoskeletal diseases, tissues primarily affected in the fibrillinopathies.The current concept of Notch signaling is based strictly on cell‐cell communication. Our investigations have the potential to transform current understanding of context‐dependent Notch signaling by introducing the possibility that Notch signaling components also interact with fibrillin extracellular matrix.Support or Funding Informationgrants from the Shriners Hospitals for Children to Lynn Y. Sakai

Fibrillin-1 in the Vasculature: In Vivo Accumulation of eGFP-Tagged Fibrillin-1 in a Knockin Mouse Model.

Immunolocalization studies have shown that fibrillin-1 is distributed ubiquitously in the connective tissue space from early embryonic times through old age. When mutated, the gene for fibrillin-1 (FBN1) causes the Marfan syndrome, a common inherited disorder of connective tissue. The multiple manifestations of the Marfan syndrome reflect the known distribution of fibrillin-1 in cardiovascular, musculoskeletal, ocular, and dermal tissues. In this study, a mouse model of Marfan syndrome in which fibrillin-1 is truncated and tagged with green fluorescence was used to estimate the relative abundance of fibrillin-1 in developing tissues. In embryonic tissues, the aorta was the only tissue in which fibrillin-1 green fluorescence was detectable. Other arteries gained detectable fibrillin-1 green fluorescence just after birth. Fibrillin-1 fluorescence was observed at later postnatal times in the lung, skin, perichondrium, tendon, and ocular tissues, while other tissues remained negative. These results indicated that tissues most affected in the Marfan syndrome are the tissues in which fibrillin-1 is most abundant. Focus was placed on the aorta, since aortic disease is life threatening in the Marfan syndrome and fibrillin-1 green fluorescence was most abundant in this tissue. Fibrillin-1 green fluorescence and immunostaining showed that fibrillin-1 is within aortic medial elastic lamellae. Endothelial-specific compared to smooth muscle-specific fibrillin-1 green fluorescence, together with light microscopic analyses of fragmentation of aortic elastic lamellae, demonstrated that smooth muscle cell mutated fibrillin-1 contributed most to progressive aortic fragmentation. However, these studies also indicated that other cells, possibly endothelial cells, also contribute to this aortic pathology. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc.

Phenotype Presentation for a Novel Mutation Affecting a Conserved Cysteine Residue in Exon 63 of Fibrillin-1 (Cys2633Arg)

Marfan syndrome is an autosomal dominant disease caused by mutations in the gene encoding for fibrillin-1 (FBN1). More than 1,000 FBN1 mutations have been identified, which may lead to multiple organ involvement, particularly of the ocular, skeletal, and cardiovascular systems. Mutations in exons 59-65 have been reported in the past to cause mild Marfan-like fibrillinopathies. We report a family with a mutation in exon 63 that manifests with significant cardiovascular system involvement such as aortic root dilatations, dissection of the aorta, and sudden death at a young age. Genetic analysis revealed that four related individuals are positive for a novel heterozygous Cys2633Arg mutation in exon 63. Their genotype-phenotype profile (based on the revised Ghent nosology) is described. We postulate that the Cys2633Arg mutation may manifest with significant and progressive enlargement of the aortic root, risk of aortic dissections, and minor skeletal abnormalities, without involving the ocular system (i.e., ectopia lentis).

Indomethacin Prevents the Progression of Thoracic Aortic Aneurysm in Marfan Syndrome Mice.

Marfan syndrome (MFS), an inherited disorder of connective tissue characterized by abnormalities in the skeletal, ocular, and cardiovascular systems, is caused by mutations in the gene for fibrillin-1 (FBN1). The high mortality in untreated patients is primarily due to aneurysm and dissection of the ascending aorta. The complex pathogenesis of MFS involves changes in transforming growth factor β (TGF-β) signaling, increased matrix metalloproteinase (MMP) expression, and fragmentation of the extracellular matrix. A number of studies have demonstrated increased counts of macrophages and T cells in the ascending aorta of persons or mouse models of MFS, but the efficacy of anti-inflammatory therapy in mouse models of MFS has not yet been assessed. FBN1 underexpressing mgR/mgR Marfan mice were treated with oral indomethacin. Treatment was begun at the age of three weeks and continued for 8 weeks, following which the aorta of wild type as well as treated and untreated mgR/mgR mice was compared. Indomethacin treatment led to a statistically significant reduction of aortic elastin degeneration and macrophage infiltration, as well as a lessening of MMP-2, MMP-9, and MMP-12 upregulation. Additionally, indomethacin decreased both cyclooxygenases 2 (COX-2) expression and activity in the aorta of mgR/mgR mice. COX-2-mediated inflammatory infiltrate contributes to the progression of aortic aneurysm in mgR/mgR mice, providing evidence that COX-2 is a relevant therapeutic target in MFS-associated aortic aneurysmal disease. COX-2 mediated inflammatory infiltration plays an important role in the pathogenesis of aortic aneurysm disease in MFS.

Development, Composition, and Structural Arrangements of the Ciliary Zonule of the Mouse

Here, we examined the development, composition, and structural organization of the ciliary zonule of the mouse. Fibrillin 1, a large glycoprotein enriched in force-bearing tissues, is a prominent constituent of the mouse zonule. In humans, mutations in the gene for fibrillin 1 (FBN1) underlie Marfan syndrome (MS), a disorder characterized by lens dislocation and other ocular symptoms. Fibrillin expression was analyzed by in situ hybridization. The organization of the zonule was visualized using antibodies to Fbn1, Fbn2, and microfibril-associated glycoprotein-1 (Magp1) in conjunction with 5-ethynyl-2'-deoxyuridine (EdU), an S-phase marker. Microfibrils, enriched in Fbn2 and Magp1, were prominent components of the temporary vascular tunic of the embryonic lens. Fbn2 expression by nonpigmented ciliary epithelial cells diminished postnatally and there was a concomitant increase in Fbn1 expression, especially in cells located in valleys between the ciliary folds. Zonular fibers projected from the posterior pars plicata to the lens in anterior, equatorial, and posterior groupings. The attachment point of the posterior zonular fibers consisted of a dense meshwork of radially oriented microfibrils that we termed the fibrillar girdle. The fibrillar girdle was located directly above the transition zone, a region of the lens epithelium in which cells commit to terminal differentiation. The development and arrangement of the murine ciliary zonule are similar to those of humans, and consequently the mouse eye may be a useful model in which to study ocular complications of MS.

Antagonism of GxxPG fragments ameliorates manifestations of aortic disease in Marfan syndrome mice

Marfan syndrome (MFS) is an inherited disorder of connective tissue caused by mutations in the gene for fibrillin-1 (FBN1). The complex pathogenesis of MFS involves changes in transforming growth factor beta (TGF-β) signaling and increased matrix metalloproteinase (MMP) expression. Fibrillin-1 and elastin have repeated Gly-x-x- Pro-Gly (GxxPG) motifs that can induce a number of effects including macrophage chemotaxis and increased MMP activity by induction of signaling through the elastin-binding protein (EBP). In this work, we test the hypothesis that antagonism of GxxPG fragments can suppress disease progression in the Marfan aorta. Fibrillin-1 underexpressing mgR/mgR Marfan mice were treated with weekly intraperitoneal (i.p.) injections of an antibody directed against GxxPG fragments. The treatment was started at 3 weeks of age and continued for 8 weeks. The treatment significantly reduced MMP-2, MMP-9 and pSmad2 activity, as well as fragmentation and macrophage infiltration in the aorta of the mgR/mgR mice. Additionally, airspace enlargement and increased pSmad2 activity in the lungs of mgR/mgR animals were prevented by the treatment. Our findings demonstrate the important role of secondary cellular events caused by GxxPG-containing fragments and matrix-induced inflammatory activity in the pathogenesis of thoracic aortic aneurysm (TAA) in mgR/mgR mice. Moreover, the results of the current study suggest that antagonism of the effects of GxxPG fragments may be a fruitful therapeutic strategy in MFS.

Skeletogenic phenotype of human Marfan embryonic stem cells faithfully phenocopied by patient-specific induced-pluripotent stem cells

Marfan syndrome (MFS) is a heritable connective tissue disorder caused by mutations in the gene coding for FIBRILLIN-1 (FBN1), an extracellular matrix protein. MFS is inherited as an autosomal dominant trait and displays major manifestations in the ocular, skeletal, and cardiovascular systems. Here we report molecular and phenotypic profiles of skeletogenesis in tissues differentiated from human embryonic stem cells and induced pluripotent stem cells that carry a heritable mutation in FBN1. We demonstrate that, as a biological consequence of the activation of TGF-β signaling, osteogenic differentiation of embryonic stem cells with a FBN1 mutation is inhibited; osteogenesis is rescued by inhibition of TGF-β signaling. In contrast, chondrogenesis is not perturbated and occurs in a TGF-β cell-autonomous fashion. Importantly, skeletal phenotypes observed in human embryonic stem cells carrying the monogenic FBN1 mutation (MFS cells) are faithfully phenocopied by cells differentiated from induced pluripotent-stem cells derived independently from MFS patient fibroblasts. Results indicate a unique phenotype uncovered by examination of mutant pluripotent stem cells and further demonstrate the faithful alignment of phenotypes in differentiated cells obtained from both human embryonic stem cells and induced pluripotent-stem cells, providing complementary and powerful tools to gain further insights into human molecular pathogenesis, especially of MFS.

Systematic screening of FBN1 gene unclassified missense variants for splice abnormalities

Defects at the level of pre-mRNA splicing are a common source of genetic mutation but such mutations are not always easy to identify from DNA sequence data alone. Clinical practice has only recently begun to incorporate analysis for this type of abnormality. Some base changes at the DNA level currently viewed as unclassified variants or missense mutations may influence RNA splicing. To address this problem for fibrillin 1 (FBN1) gene missense mutations we have carried out RNA analysis and in silico analysis with splice site prediction programs on 40 cases with 36 different mutations. Direct analysis of RNA from blood was performed by cDNA preparation, PCR amplification of specific FBN1 fragments, gel electrophoresis and sequencing of the PCR products. Of the 36 missense base changes, direct RNA analysis identified 2 which caused an abnormality of splicing. In silico analysis using five splice site prediction programs did not always accurately predict the splicing seen by direct RNA analysis. In conclusion, some apparent missense mutations have an effect on splicing which can be identified by direct RNA analysis, however, in silico analysis of splice sites is not always accurate, should be carried out with more than one prediction program and results should be used with caution.

Homozygosity for a FBN1 missense mutation: clinical and molecular evidence for recessive Marfan syndrome

Marfan syndrome (MFS) is known as an autosomal-dominant connective tissue disorder (MIM 154,700), involving primarily the skeletal, ocular and cardiovascular systems, and caused by mutations in the gene for fibrillin1 (FBN1). Here, we report on two cousins from a consanguineous family with a homozygous c.1,453C>T FBN1 mutation (p.Arg485Cys) and MFS. All four healthy parents were heterozygous for the c.1,453C>T FBN1 mutation and none fulfilled the Ghent criteria for MFS. This family is the first molecularly confirmed recessive MFS. The demonstration of recessive cases of MFS has obvious implications for genetic counselling as well as for molecular diagnosis.

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.

Three novel mutations of the fibrillin-1 gene and ten single nucleotide polymorphisms of the fibrillin-3 gene in Marfan syndrome patients.

Marfan syndrome (MFS) is an autosomal dominant disorder of the extracellular matrix. Allelic variations in the gene for fibrillin-1 ( FBN1) have been shown to cause MFS. To date, over 550 mutations have been identified in patients with MFS and related connective tissue diseases. However, about a half of MFS cases do not possess mutations in the FBN1 gene. These findings raise the possibility that variants located in other genes cause or modify MFS. To explore this possibility, firstly we analyzed FBN1 allelic variants in 12 Japanese patients with MFS, and secondly we analyzed fibrillin-3 gene ( FBN3) in patients without FBN1 mutations using conformation sensitive gel electrophoresis (CSGE) and direct sequencing analysis. We identified three novel FBN1 mutations and ten FBN3 single nucleotide polymorphisms (SNPs). In this report, we could not detect a responsible mutation of the FBN3 gene for MFS. Although the number of the cases in this report is small, at least these results suggest that disease-causing mutations in exon regions of the FBN3 gene are very rare in MFS.

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.

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.

Genotype and phenotype analysis of 171 patients referred for molecular study of the fibrillin-1 gene FBN1 because of suspected Marfan syndrome.

Marfan syndrome (MFS) is an underrecognized heritable connective tissue disorder resulting from mutations in the gene for fibrillin-1 (FBN1). Affected patients are at risk for aortic dissection and/or severe ocular and orthopedic problems. The diagnosis is primarily based on a set of well-defined clinical criteria (Ghent nosology). The age-related nature of some clinical manifestations and variable phenotypic expression may hinder the diagnosis, particularly in children. Molecular analysis may be helpful to identify at-risk individuals early and start prophylactic medical treatment. FBN1 mutations have also been reported in patients with Marfan-related conditions, but it is unknown what proportion of all FBN1 mutation carriers they represent. We reviewed the clinical and molecular data of 171 consecutive patients referred for FBN1 analysis because either MFS was diagnosed or they had signs suggestive of MFS. We compared the incidence of mutations in patients who fulfilled the clinical diagnostic criteria for MFS with those who did not. Diagnostic criteria for MFS were fulfilled in 94 patients, 62 (66%) of whom had an FBN1 mutation. A significantly higher incidence of ectopia lentis was found in the patients with MFS with an FBN1 mutation vs those without (P=.04). Among the 77 patients who did not meet the criteria, an FBN1 mutation was found in 9 patients (12%). No correlation was found between the severity of the phenotype and the position and nature of the FBN1 mutation. This study showed a significant difference in the number of FBN1 mutations between patients fulfilling and those not fulfilling the diagnostic criteria for MFS, which seems to be a good predictor of the presence of an FBN1 mutation. A comprehensive clinical evaluation is mandatory before establishing a definitive diagnosis. An FBN1 mutation analysis is helpful to identify individuals at high risk for MFS who need careful follow-up, particularly in families displaying phenotypic variability and in children.

The molecular pathogenesis of the Marfan syndrome.

The Marfan syndrome (MFS) is an autosomal dominant heritable disorder of connective tissue with highly variable clinical manifestations including aortic dilatation and dissection, ectopia lentis, and a range of skeletal anomalies. Mutations in the gene for fibrillin-1 (FBN1) cause MFS and other related disorders of connective tissue collectively termed type-1 fibrillinopathies. Fibrillin-1 is a main component of the 10- to 12-nm extracellular microfibrils that are important for elastogenesis, elasticity, and homeostasis of elastic fibers. Mutations in fibrillin-1 are hypothesized to exert their effects by dominant negative mechanisms, but recent work has also emphasized the potential role of proteases and disturbances in tissue homeostasis in the pathogenesis of the MFS. This article provides an overview of the clinical aspects of the MFS and current thinking on the pathogenesis of this disorder.

Classic, atypically severe and neonatal Marfan syndrome: twelve mutations and genotype-phenotype correlations in FBN1 exons 24-40.

Mutations in the gene for fibrillin-1 (FBN1) cause Marfan syndrome, an autosomal dominant disorder of connective tissue with prominent manifestations in the skeletal, ocular, and cardiovascular system. There is a remarkable degree of clinical variability both within and between families with Marfan syndrome as well as in individuals with related disorders of connective tissue caused by FBN1 mutations and collectively termed type-1 fibrillinopathies. The so-called neonatal region in FBN1 exons 24-32 comprises one of the few generally accepted genotype-phenotype correlations described to date. In this work, we report 12 FBN1 mutations identified by temperature-gradient gel electrophoresis screening of exons 24-40 in 127 individuals with Marfan syndrome or related disorders. The data reported here, together with other published reports, document a significant clustering of mutations in exons 24-32. Although all reported mutations associated with neonatal Marfan syndrome and the majority of point mutations associated with atypically severe presentations have been found in exons 24-32, mutations associated with classic Marfan syndrome occur in this region as well. It is not possible to predict whether a given mutation in exons 24-32 will be associated with classic, atypically severe, or neonatal Marfan syndrome.

Elastic-Fiber Pathologies: Primary Defects in Assembly—and Secondary Disorders in Transport and Delivery

Accession numbers and the URL for data in this article are as follows:Online Mendelian Inheritance in Man (OMIM), www.ncbi.nlm.nih.gov/Omim (for congenital contractural arachnodactyly [MIM 121050], adCL [MIM 123700], MFS [MIM 154700]), SVAS [MIM 185500], Williams-Beuren syndrome [MIM 194050], Costello syndrome [MIM 218040], GM1-gangliosidosis [MIM 230500, MIM 230600, and MIM 230650], MPSI [MIM 252800], and MPS IVB [MIM 253010])