Related Connective Tissue Disorders Research Articles

Cerebral Microvascular Density, Permeability of the Blood-Brain Barrier, and Neuroinflammatory Responses Indicate Early Aging Characteristics in a Marfan Syndrome Mouse Model.

Marfan Syndrome (MFS) is a connective tissue disorder due to mutations in fibrillin-1 ( Fbn1 ), where a Fbn1 missense mutation ( Fbn1 C1039G/+ ) can result in systemic increases in the bioavailability and signaling of transforming growth factor-β (TGF-β). In a well-established mouse model of MFS ( Fbn1 C1041G/+ ), pre-mature aging of the aortic wall and the progression of aortic root aneurysm are observed by 6-months-of-age. TGF-β signaling has been implicated in cerebrovascular dysfunction, loss of blood-brain barrier (BBB) integrity, and age-related neuroinflammation. We have reported that pre-mature vascular aging in MFS mice could extend to cerebrovasculature, where peak blood flow velocity in the posterior cerebral artery (PCA) of 6-month-old (6M) MFS mice was reduced, similarly to 12-month-old (12M) control mice. Case studies of MFS patients have documented neurovascular manifestations, including intracranial aneurysms, stroke, arterial tortuosity, as well as headaches and migraines, with reported incidence of pain and chronic fatigue. Despite these significant clinical observations, investigation into cerebrovascular dysfunction and neuropathology in MFS remains limited. Using 6M-control ( C57BL/6 ) and 6M-MFS ( Fbn1 C1041G/+ ) and healthy 12M-control male and female mice, we test the hypothesis that abnormal Fbn1 protein expression is associated with altered cerebral microvascular density, BBB permeability, and neuroinflammation in the PCA-perfused hippocampus, all indicative of a pre-mature aging brain phenotype. Using Glut1 staining, 6M-MFS mice and 12M-CTRL similarly present decreased microvascular density in the dentate gyrus (DG), cornu ammonis 1 (CA1), and cornu ammonis 3 (CA3) regions of the hippocampus. 6M-MFS mice exhibit increased BBB permeability in the DG, CA1, and CA3 as evident by Immunoglobulin G (IgG) staining, which was more comparable to 12M-CTRL mice. 6M-MFS mice show a higher number of microglia in the hippocampus compared to age-matched control mice, a pattern resembling that of 12M-CTRL mice. This study represents the first known investigation into neuropathology in a mouse model of MFS and indicates that the pathophysiology underlying MFS leads to a systemic pre-mature aging phenotype. This study is crucial for identifying and understanding MFS-associated neurovascular and neurological abnormalities, underscoring the need for research aimed at improving the quality of life and managing pre-mature aging symptoms in MFS and related connective tissue disorders.

Investigation of dermal collagen nanostructures in Ehlers-Danlos Syndrome (EDS) patients.

Ehlers-Danlos syndromes (EDS) represent a group of rare genetic disorders affecting connective tissues. Globally, approximately 1.5 million individuals suffer from EDS, with 10,000 reported cases in Canada alone. Understanding the histological properties of collagen in EDS has been challenging, but advanced techniques like atomic force microscopy (AFM) have opened up new possibilities for label-free skin imaging. This approach, which explores Type I collagen fibrils at the nanoscale, could potentially enhance EDS diagnosis and our knowledge of collagen type I-related connective tissue disorders. In the current study, we have employed AFM to examine ex-vivo skin biopsies from four individuals: one with classical EDS (cEDS), one with hypermobile EDS (hEDS), one with hEDS and Scleroderma (hEDS-Scleroderma), and one healthy control. Picrosirius red (PS) staining was used to highlight collagen differences in the samples. For each case, 14 images and 1400 force curves were obtained, with seven images and 700 force curves representing healthy collagen (PS-induced red staining) and the rest showcasing disrupted collagen (yellow staining). The results showed that PS staining was uniform throughout the control section, while cEDS and hEDS displayed localized areas of yellow staining. In the case of hEDS-Scleroderma, the yellow staining was widespread throughout the section. AFM images revealed irregular collagen fibrils in the disrupted, yellow-stained areas, contrasting with aligned and well-registered collagen fibrils in healthy, red-stained regions. Additionally, the study assessed the ability of non-AFM specialists to differentiate between healthy and disrupted collagen in AFM images, yielding substantial agreement among raters according to Fleiss's and Cohen's kappa scores (0.96 and 0.79±0.1, respectively). Biomechanical analysis revealed that normal healthy collagen exhibited a predominant population at 2.5 GPa. In contrast, EDS-affected collagen displayed subpopulations with lower compressive elastic modulus, indicating weaker collagen fibrils in EDS patients. Although these findings pertain to a limited number of cases, they offer valuable insights into the nanoscale collagen structure and biomechanics in individuals with EDS. Over time, these insights could be developed into specific biomarkers for the condition, improving diagnosis and treatment for EDS and related connective tissue disorders.

Multidisciplinary Approach to Treating Chronic Pain in Patients with Ehlers-Danlos Syndrome: Critically Appraised Topic.

The Ehlers–Danlos syndromes (EDS) are a group of 13 related connective tissue disorders with a combined prevalence of 1 in 5000 people, with the most common noted as hypermobile EDS (hEDS). The EDS genetic condition is thought to affect both males and females equally, although most symptomatic patients are female. EDS causes a myriad of symptoms, including skin hyperextensibility and fragility, easy bruising and bleeding, joint hypermobility, subluxation, dislocation, and chronic pain. Pain is one of the most common symptoms of EDS, leading to disability and decreased quality of life. Current guidelines for treating chronic pain in EDS are lacking. Clinicians focus on a conservative multidisciplinary approach in patients with EDS, which avoids surgical interventions and its accompanying risks of morbidity and mortality. The multidisciplinary approach includes physiotherapy, occupational therapy, cognitive behavioral therapy, and pharmacologic interventions to decrease pain. This review identifies literature examining the components of this conservative multidisciplinary approach and their effectiveness across the PubMed, EMBASE, CINAHL, Web of Science, and Trip databases, using the terms “Ehlers-Danlos Syndrome AND Pain Management” that was then subsequently evaluated. The evaluation of this current literature provides weak evidence to support the efficacy of the individual components of the conservative multidisciplinary approach. Lack of alternative approaches leaves medical providers with little choice but to suggest these pain control methods, despite low-grade evidence of weak evidence of their efficacy. More research into the pathophysiology of chronic pain in EDS could help identify additional modes and rationales for therapy.

Association of mast-cell-related conditions with hypermobile syndromes: a review of the literature.

Ehlers–Danlos syndrome (EDS) is a group of related connective tissue disorders consisting of 13 subtypes, each with its own unique phenotypic and genetic variation. The overlap of symptoms and multitude of EDS variations makes it difficult for patients to achieve a diagnosis early in the course of their disease. The most common form, hypermobile type EDS (hEDS) and its variant, hypermobile spectrum disorder (HSD), are correlated with rheumatologic and inflammatory conditions. Evidence is still needed to determine the pathophysiology of hEDS; however, the association among these conditions and their prevalence in hEDS/HSD may be explained through consideration of persistent chronic inflammation contributing to a disruption of the connective tissue. Aberrant mast cell activation has been shown to play a role in disruption of connective tissue integrity through activity of its mediators including histamine and tryptase which affects multiple organ systems resulting in mast cell activation disorders (MCAD). The overlap of findings associated with MCAD and the immune-mediated and rheumatologic conditions in patients with hEDS/HSD may provide an explanation for the relationship among these conditions and the presence of chronic inflammatory processes in these patients. It is clear that a multidisciplinary approach is required for the treatment of patients with EDS. However, it is also important for clinicians to consider the summarized symptoms and MCAD-associated characteristics in patients with multiple complaints as possible manifestations of connective tissue disorders, in order to potentially aid in establishing an early diagnosis of EDS.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12026-022-09280-1.

Marfan syndrome and related connective tissue disorders in the current era in Switzerland in 103 patients: medical and surgical management and impact of genetic testing.

Marfan syndrome (MFS) and related connective tissue disorders (CTDs) are increasingly recognised. Genetic testing has greatly improved the diagnostic outcome/power over the last two decades. In this study we describe a multicentre cohort of adults with MFS and related CTDs, with a particular focus on results from genetic testing. All patients with MFS and related CTDs were identified from the databases of five centres in the canton of Zurich. Echocardiographic and clinical findings including systemic Marfan score, use of medication and genetic results were retrospectively analysed. MFS was diagnosed using the revised Ghent criteria (including FBN1 genetic testing if available); other CTDs (Loeys-Dietz syndrome) were diagnosed by genetic testing only. A cohort of 103 patients were identified (62 index patients, 41 relatives of family members): 96 patients with MFS and 7 patients with other CTD, 54 males (52%), median age 23 years (range 1–75). The median systemic Marfan score was 5 (range 0–18). Only 40 patients (40/103, 39%) fulfilled criteria for systemic involvement (≥7 points). A history of aortic dissection was present in 14 out of 103 patients (14%). Echocardiographic data were available for all: aortic root enlargement (Z-score ≥2 in adults, Z-score ≥3 in children) was found in 49 patients (48%) and mitral valve prolapse in 64 (62%). Genetic testing had been performed in 80 patients (78%); FBN1 mutations were present in 69 patients (86%); other pathogenic mutations could be identified in seven patients (9%); no disease-causing mutation was found in four patients, three of them fulfilling the Ghent criteria of MFS. Of the mutation-positive patients, 33 had a systemic score of ≥7 and 43 had a systemic score of ≥5. Revised Ghent criteria were fulfilled in 70 patients: in 69 patients with FBN1 mutations and 1 patient with another CTD. Recommended treatment (beta-blocker, angiotensin receptor blocker) was taken by 63% of patients. In this cohort a high percentage of patients fulfilling the revised Ghent criteria for MFS underwent genetic testing, often leading to or confirming the diagnosis of MFS. Other CTDs could be discriminated best by genetic testing. With respect to the diagnosis of MFS and related CTDs, the usefulness of the systemic score is limited, showing the importance of genetic testing, which enabled definitive diagnosis in 95% of tested patients. Patient education on medical treatment still has to be improved. (Trial registration no: KEK-ZH-Nr. 2013-0241).

Therapeutic and diagnostic advances in Stickler syndrome.

Treatment and diagnostic advances in Stickler syndrome The Stickler syndromes are a group of related connective tissue disorders that are associated with short-sight and a very high risk of blindness from detachment of the retina - the light sensitive film at the back of the eye. Other features include cleft palate, deafness and premature arthritis. It is the most common cause of retinal detachment in children and the most common cause of familial or inherited retinal detachment. In contrast to most other forms of blinding genetic eye disease, blindness from retinal detachment in Stickler syndrome is largely avoidable with accurate diagnosis and prophylactic (preventive) surgery. Recent advances in the understanding of the genetic causes of Stickler syndrome mean that the diagnosis can now be confirmed in over 95% of cases and, most importantly, the patient's individual risk of retinal detachment can be graded. Preventative surgery is hugely effective in reducing the incidence of retinal detachment in those patients shown to be at high risk. NHS England have led the way in the multidisciplinary care for patients with Stickler syndrome by launching a highly specialist service that has been free at point of care to all NHS patients in England since 2011 (https://www.england.nhs.uk/commissioning/spec-services/highly-spec-services, www.vitreoretinalservice.org).

Colonoscopy is safe and not associated with higher pain scores in patients with hypermobility spectrum disorder: results from an exploratory prospective study.

Background:Patient perception of colonoscopy varies greatly. Young slender women and patients with irritable bowel syndrome (IBS) appear to be at risk for periprocedural pain. Recent evidence suggests a high prevalence of joint hypermobility related connective tissue disorders in this population. Therefore, we aimed to investigate whether hypermobility spectrum disorder (HSD) is associated with increased pain during colonoscopy.Methods:We prospectively included patients undergoing routine colonoscopy. Subjects were assessed for HSD using the 2017 criteria, and IBS and functional dyspepsia using the Rome III criteria. After colonoscopy and recovery from sedation, patients were asked to report pain scores on a 100-mm visual analogue scale (VAS). In addition, caecal intubation time was measured, endoscopists scored the difficulty of the procedure (100-mm VAS) and procedure-related adverse events were registered.Results:Of 200 included patients, 22 (11%) met criteria for HSD. A female predominance was observed in patients with HSD (86.4% versus 49.4%, p < 0.001). A crude linear regression model demonstrated that pain scores were 13.30 mm higher in patients with HSD versus non-HSD patients (95% CI 0.07 – 26.53, p = 0.049). When subsequently correcting for possible confounding factors, however, this difference in pain scores could be explained by a confounding effect of female gender. Caecal intubation time, perceived procedural difficulty and complication rate did not differ significantly between groups.Conclusion:HSD does not seem to be a predictor of painful colonoscopy, probably due to female gender as a confounding factor. In addition, performing colonoscopy is not more complicated in patients with HSD versus non-HSD patients, nor is it associated with more adverse events.

FBN1 gene mutations in 26 Hungarian patients with suspected Marfan syndrome or related fibrillinopathies

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder mainly affecting the cardiovascular, ocular and musculo-skeletal systems. FBN1 gene mutations lead to MFS and related connective tissue disorders. In this work we described clinical and molecular data of 26 unrelated individuals with suspected MFS who were referred for FBN1 mutation analysis. FBN1 gene sequencing was performed by next generation sequencing and Sanger sequencing methods. We identified 23 causal or potentially causal (including variants of uncertain significance) FBN1 variants, seven of them was novel (˜30%). About 30% of the cases were sporadic. FBN1 mutations were associated with MFS in the majority of the patients, in two cases with severe and early onset manifestation of the syndrome. Missense mutations were detected in 69.6% (16/23), the majority of them were located in one of the cbEGF motifs and ˜70% of them substituted conserved cystein residues. Small deletions/duplications were identified in 13% of the cases (3/23), while splice site variants were detected in 17.4% (4/23). In three unrelated patients a low frequency recurrent silent variant (c.3294C > T (p.Asp1098=) was identified. FBN1 mRNA analysis showed that the mutation does not lead to aberrant splicing, based on available data the mutation was classified as benign.

Qualitative and quantitative analysis of FBN1 mRNA from 16 patients with Marfan Syndrome

BackgroundPathogenic mutations in FBN1, encoding the glycoprotein, fibrillin-1, cause Marfan syndrome (MFS) and related connective tissue disorders. In the present study, qualitative and quantitative effects of 16 mutations, identified in FBN1 in MFS patients with systematically described phenotypes, were investigated in vitro.MethodsQualitative analysis was performed with reverse transcription-PCR (RT-PCR) and gel electrophoresis, and quantitative analysis to determine the FBN1 mRNA levels in fibroblasts from the 16 patients with MFS was performed with real-time PCR.ResultsQualitative analysis documented that the mutations c.4817-2delA and c.A4925G led to aberrant FBN1 mRNA splicing leading to in frame deletion of exon 39 and in exon 39, respectively. No difference in the mean FBN1 mRNA level was observed between the entire group of cases and controls, nor between the group of patients with missense mutations and controls. The mean expression levels associated with premature termination codon (PTC) and splice site mutations were significantly lower than the levels in patients with missense mutations. A high level of FBN1 mRNA in the patient with the missense mutation c.G2447T did not segregate with the mutation in three of his first degree relatives. No association was indicated between the FBN1 transcript level and specific phenotypic manifestations.ConclusionsAbnormal FBN1 transcripts were indicated in fibroblasts from patients with the splice site mutation c.4817-2delA and the missense mutation c.A4925G. While the mean FBN1 mRNA expression level in fibroblasts from patients with splice site and PTC mutations were lower than the mean level in patients with missense mutations and controls, inter-individual variability was high. The observation that high level of FBN1 mRNA in the patient with the missense mutation c.G2447T did not segregate with the mutation in the family suggests that variable expression of the normal FBN1 allele may contribute to explain the variability in FBN1 mRNA level.Electronic supplementary materialThe online version of this article (doi:10.1186/s12881-015-0260-4) contains supplementary material, which is available to authorized users.

Clinical Stratification of Pediatric Patients with Idiopathic Thoracic Aortic Aneurysm

To describe the global phenotypes of pediatric patients with thoracic aortic aneurysm (TAA) who do not have a clinical diagnosis of Marfan syndrome (MFS) or related connective tissue disorders. We hypothesized that the presence of noncardiovascular abnormalities correlate with TAA severity and that medical therapy reduces TAA progression. This is a retrospective case series of patients with TAA age ≤ 21 years evaluated in a cardiovascular genetics clinic. Patients meeting clinical criteria for MFS or related disorders were excluded. Repeated measures analyses of longitudinal echocardiographic measurements of the aorta were used to test associations between TAA severity and noncardiovascular phenotype and to assess the impact of medical therapy. Sixty-nine patients with TAA at mean age 12.5 ± 5.3 years were included. Noncardiovascular abnormalities, including skeletal (65%) or craniofacial (54%) findings, were frequently observed. Increased rate of aortic root enlargement was associated with ocular (P = .002) and cutaneous (P = .003) abnormalities, and increased rate of ascending aorta enlargement was associated with craniofacial (P < .001) abnormalities. Beta blocker or angiotensin receptor blocker therapy (n = 41) was associated with reduction in the rate of aortic root growth (P = .018). Children with TAA not satisfying diagnostic criteria for MFS or related disorders frequently have noncardiovascular findings, some of which are associated with TAA progression. Because therapy initiation may reduce risk of progression and long-term complications, comprehensive assessment of noncardiovascular findings may facilitate early risk stratification and improve outcomes.

Two novel distinct COL1A2 mutations highlight the complexity of genotype–phenotype correlations in osteogenesis imperfecta and related connective tissue disorders

Osteogenesis imperfecta is a heritable connective tissue disorder characterized by variable symptoms including predisposition to fractures. Despite the identification of numerous mutations, a reliable genotype–phenotype correlation has remained notoriously difficult. We now describe two patients with osteogenesis imperfecta and novel, so far undescribed mutations in the COL1A2 gene, further highlighting this complexity. A 3-year-old patient presented with features reminiscent of a connective tissue disorder, with joint hypermobility, Wormian bones, streaky lucencies in the long bones and relative macrocephaly. The patient carried a heterozygous c.1316G > A (p.Gly439Asp) mutation in the COL1A2 gene located in a triple-helix region, in which glycine substitutions have been assumed to cause perinatal lethal OI (Sillence type II). A second family with type I osteogenesis imperfecta carried a heterozygous nonsense mutation c.4060C > T (p.Gln1354X) within the last exon of COL1A2. Whereas other heterozygous nonsense mutations in COL1A2 do not lead to a phenotype, in this case the mRNA is presumed to escape nonsense-mediated decay. Therefore the predicted COL1A2 propeptide lacks the last 13 C-terminal amino acids, suggesting that the OI phenotype results from decelerated assembly and overmodification of the collagen triple helix. The presented COL1A2 mutations exemplify the complexity of COL1A2 genotype–phenotype correlation in genetic counselling in OI.

Biophysical properties of the aorta in patients with Marfan syndrome and related connective tissue disorders: evaluation with MRI and computational fluid dynamics modeling

Objective The purpose of this study was to evaluate the biophysical properties of the aorta in patients with Marfan Syndrome or Loeys-Dietz Syndrome using MRI and computational fluid dynamics (CFD) modeling. Background Patients with Marfan Syndrome and related disorders have abnormal wall properties throughout the thoracic aorta including low distensibility in areas that eventually dilate. CFD modeling based on MRI data can be used to quantify distensibility and indices such as velocity and wall shear stress (WSS) throughout the cardiac cycle and for the entire thoracic aorta. We sought to use cardiac MRI and CFD modeling to evaluate the distensibility and indices of WSS in the aorta of patients with Marfan Syndrome and related disorders compared to age- and gender-matched controls. Methods Patients with Marfan Syndrome or a related disorder and no history of surgery who underwent a recent MRI were identified (n=6; 5 Marfan, 1 Loeys-Dietz). After measuring blood pressure, aortic wall dimensions and distensibility were calculated off-line by two independent observers at 3 locations: ascending aorta (AAo), thoracic descending aorta (DAoT), and descending aorta at the level of the diaphragm (DAoD). CFD simulations were performed using a stabilized finite element solver and incorporated downstream vascular resistance and compliance CFD models to quantify time-averaged WSS (TAWSS) and oscillatory shear index (OSI) throughout the aorta. Results

TGF-beta-dependent mechanisms of patho genesis of Marfan syndrome and related disorders

Recent research on the molecular physiology of fibrillin and the pathophysiology of Marfan syndrome and related connective tissue disorders has changed our understanding of this pathology by demonstrating changes in growth factor signalling and in matrix-cell interactions. Marfan syndrome is an autosomal dominant disorder of connective tissue caused by mutations in fibrillin-1. Fibrillin-1 contributes to the regulated activation of the cytokine TGF-ß, and enhanced signaling is a consequence of fibrillin-1 deficiency. Thereby, increased TGF-ß signaling may contribute to the multisystem pathogenesis of Marfan syndrome, including the development of myxomatous changes of the atrioventricular valve, aortic aneurysm and dissection, joint hypermobility syndrome. These data suggest that anti-TGF-β therapeutic strategy for patients with Marfan syndrome can be useful in prevention of the major life-threatening manifestation of this disorder.

Detection of 53 FBN1 mutations (41 novel and 12 recurrent) and genotype–phenotype correlations in 113 unrelated probands referred with Marfan syndrome, or a related fibrillinopathy

Mutations in the gene encoding fibrillin 1 (FBN1) cause Marfan syndrome (MFS), and related connective tissue disorders. The disease spectrum is wide and while many genotype-phenotype correlations have been reported, few have been consistent. In this study FBN1 was analyzed in 113 patients with MFS or Marfan-like features. Fifty-three mutations were identified in 52 individuals, 41 of which were novel. The mutations comprised 26 missense, 11 splice site, 7 frameshift, 6 nonsense, 1 in-frame deletion, and 2 whole exon deletions. In common with previous studies, genotype-phenotype analysis showed that a FBN1 mutation was more likely to be identified in patients fulfilling Ghent criteria (P = 0.005) and in those who had ectopia lentis (EL) (P < 0.0001). Other previously reported genotype-phenotype correlations were also considered and a new inverse association between a mutation in exons 59-65, and EL emerged (P = 0.002).

Fibrillin‐rich microfibrils: Structural determinants of morphogenetic and homeostatic events

Fibrillin-rich microfibrils are specialized extracellular matrix assemblies that endow connective tissues with mechanical stability and elastic properties, and that participate in the regulation of organ formation, growth and homeostasis. Their physiological importance is underscored by the complex spectrum of clinical manifestations associated with mutations of fibrillin-1 and fibrillin-2 in Marfan syndrome (MFS) and congenital contractural arachnodactyly, respectively. Early evidence suggested that fibrillin-1 mutations in MFS lead to loss of tissue integrity by perturbing microfibril assembly and function. Recent studies in genetically targeted mice have however revealed that fibrillin-1 and fibrillin-2 mutations perturb signaling events mediated by TGF-beta superfamily members. As such, these studies have established a new biological paradigm whereby fibrillin-rich microfibrils are structural networks that specify the local concentration and timely release of signaling molecules during morphogenesis and tissue remodeling. This review summarizes our current understanding of the role of fibrillin-rich microfibrils in development and disease, as well as exciting new applications in the clinical management of MFS and related connective tissue disorders.

Cost‐effective screening method for antinuclear antibody detection

AbstractAim: To evaluate indirect immunoenzyme (IIE) technique, for detection of antinuclear antibodies (ANA) using serum and filter paper blood clots (FPBC) especially for screening.Methods: Antinuclear antibody processing from FPBC (prepared by expressing blood drops by finger pricking) was standardized in a pilot study. Paired samples (serum and corresponding FPBC) from 224 individuals [142 patients of systemic rheumatic diseases, chiefly lupus and rheumatoid arthritis (RA) and 82 healthy controls (HC)] were tested by the standard immunofluorescence (IIF) and IIE (using light microscope); samples were coded, blinded and randomly processed as per the protocol. End‐point titres were determined for positive serum samples only. Standard reagents (Immunoconcepts Incorporation, US) and controls (CDC, Atlanta, US) were used. All patients were identified in a rheumatology referral practice in an Indian metropolis.Results: The sensitivity of IIE and IIF for SLE, using serum and FPBC was ≈90%. The specificity of IIE and IIF for SLE, using serum and FPBC was in the range 66–73% and 58–63%, respectively. Good–perfect agreement (κ &gt; 0.8) between the results was obtained by IIE and IIF for all groups except RA. Except the RA group, all other paired samples showed good concordance (72%) on testing for ANA patterns by both techniques.Conclusions: Indirect immunoenzyme technique is a robust technique and should be considered a viable option to IIF at least in countries like India; its further use on FPBC is a socioeconomically appealing proposition for carrying out population studies on lupus and related uncommon connective tissue disorders.

Defective secretion of recombinant fragments of fibrillin-1: implications of protein misfolding for the pathogenesis of Marfan syndrome and related disorders.

Fibrillin-1 is a large modular glycoprotein that assembles to form 10-12 nm microfibrils in the extracellular matrix. Mutations in the fibrillin-1 gene (FBN1) cause Marfan syndrome and related connective tissue disorders (fibrillinopathies) that show autosomal dominant inheritance. The pathogenic mechanism is thought to be a dominant negative effect of a mutant protein on microfibril assembly, although direct evidence is lacking. A significant group of disease-causing FBN1 mutations are cysteine substitutions within EGF domains that are predicted to cause misfolding by removal of disulphide bonds that stabilize the native domain fold. We have studied three missense mutations (C1117Y, C1129Y and G1127S) to investigate the effect of misfolding on the trafficking of fibrillin-1 from fibroblast cells. We demonstrate that both C1117Y and C1129Y, expressed as recombinant fragments of fibrillin-1, are retained and accumulate within the cell. Both undergo core glycosylation but lack the complex glycosylation observed in the secreted wild-type fragment, suggesting retention in the endoplasmic reticulum (ER). In addition, co-immunoprecipitation experiments show association with the ER chaperone calreticulin, but not calnexin, 78 kDa glucose-regulated protein (Grp78/BiP) or protein disulfide isomerase. In contrast, G1127S, which causes a moderate change in the EGF domain fold, shows a pattern of glycosylation and trafficking profile indistinguishable from the wild-type fragment. Since expression of the recombinant fragments does not disrupt the secretion of endogenous fibrillin-1 by the cell, we propose that G1127S causes disease via an extracellular dominant negative effect. In contrast, the observed ER retention of C1117Y and C1129Y suggests that disease associated with these missense mutations is caused either by an intracellular dominant negative effect or haploinsufficiency.

Mutation screening of the fibrillin-1 (FBN1) gene in 76 unrelated patients with Marfan syndrome or Marfanoid features leads to the identification of 11 novel and three previously reported mutations.

Mutations in the gene encoding fibrillin-1 (FBN1) cause Marfan syndrome (MFS) and other related connective tissue disorders. In this study we performed SSCP to analyze all 65 exons of the FBN1 gene in 76 patients presenting with classical MFS or related phenotypes. We report 7 missense mutations, 3 splice site alterations, one indel mutation, one nonsense mutation and two mutations causing frameshifts: a 16bp deletion and a single nucleotide insertion. 5 of the missense mutations (Y1101C, C1806Y, T1908I, G1919D, C2251R) occur in calcium-binding Epidermal Growth Factor-like (EGFcb) domains of exons 26, 43, 46 and 55, respectively. One missense mutation (V449I) substitutes a valine residue in the non-calcium-binding epidermal growth factor like domain (EGFncb) of exon 11. One missense mutation (G880S) affects the "hybrid" motif in exon 21 by replacing glycine to serine. The 3 splice site mutations detected are: IVS1-1G>A in intron 1, IVS38-1G>A in intron 38 and IVS46+5G>A in intron 46. C628delinsK was identified in exon 15 leading to the substitution of a conserved cysteine residue. Furthermore two frameshift mutations were found in exon 15 (1904-1919del ) and exon 63 (8025insC) leading to premature termination codons (PTCs) in exon 17 and 64 respectively. Finally we identified a nonsense mutation (R429X) located in the proline rich domain in exon 10 of the FBN1 gene. Y1101C, IVS46+5G>A and R429X have been reported before.

Fibrillin: from microfibril assembly to biomechanical function.

Fibrillins form the structural framework of a unique and essential class of extracellular microfibrils that endow dynamic connective tissues with long-range elasticity. Their biological importance is emphasized by the linkage of fibrillin mutations to Marfan syndrome and related connective tissue disorders, which are associated with severe cardiovascular, ocular and skeletal defects. These microfibrils have a complex ultrastructure and it has proved a major challenge both to define their structural organization and to relate it to their biological function. However, new approaches have at last begun to reveal important insights into their molecular assembly, structural organization and biomechanical properties. This paper describes the current understanding of the molecular assembly of fibrillin molecules, the alignment of fibrillin molecules within microfibrils and the unique elastomeric properties of microfibrils.

Clustering of mutations associated with mild Marfan-like phenotypes in the 3? region ofFBN1 suggests a potential genotype-phenotype correlation

Mutations in the gene for fibrillin-1 (FBN1) cause Marfan syndrome, a dominantly inherited disorder of connective tissue that primarily involves the cardiovascular, ocular, and skeletal systems. There is a remarkable degree of variability both within and between families with Marfan syndrome, and FBN1 mutations have also been found in a range of other related connective tissue disorders collectively termed type-1 fibrillinopathies. FBN1 mutations have been found in almost all of the 65 exons of the FBN1 gene and for the most part have been unique to one affected patient or family. Aside from the "hot spots" for the neonatal Marfan syndrome in exons 24-27 and 31-32, genotype-phenotype correlations have been slow to emerge. Here we present the results of temperature-gradient gel electrophoresis analysis of FBN1 exons 59-65. Six mutations were identified, only one of which had been previously reported. Two of the six mutations were found in patients with mild phenotypes. Taken together with other published reports, our results suggest that a sizable subset (ca. 40%) of mutations in this region is associated with mild phenotypes characterized by the lack of significant aortic pathology, compared with about 7% in the rest of the gene. In two cases, mutations affecting analogous positions within one of the 43 cbEGF modules of FBN1 are associated with mild phenotypes when found in one of the 6 C-terminal modules (encoded by exons 59-63), but are associated with classic or severe phenotypes when found in cbEGF modules elsewhere in the gene.