Marfan syndrome: from molecular pathogenesis to clinical treatment

A novel de novo intragenic duplication in FBN1 associated with early-onset Marfan syndrome in a 16-month-old: A case report and review of the literature

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder due to pathogenic variants in Fibrillin-1 (FBN1) affecting nearly one in every 10,000 individuals. We report a 16-month-old female with early-onset MFS heterozygous for an 11.2 kb de novo duplication within the FBN1 gene. Tandem location of the duplication was further confirmed by optical genome mapping in addition to genetic sequencing and chromosomal microarray. This is the third reported case of a large multi-exon duplication in FBN1, and the only one confirmed to be in tandem. As the vast majority of pathogenic variants associated with MFS are point mutations, this expands the landscape of known FBN1 pathogenic variants and supports consistent use of genetic testing strategies that can detect large, indel-type variants.

Concomitant uterus agenesia and Marfan syndrome with systemic sclerosis: A rare case report

It seems that the association of two connective tissue disorders, including Marfan syndrome and systemic sclerosis, the first is associated with the loosening of the subcutaneous tissue and the second with its tightening, is a very interesting and controversial paradox at the same time and need finding possible genetic etiologies.

Heart transplantation in neonatal Marfan syndrome: Saving life in a rare and fatal condition

BACKGROUND

Neonatal Marfan syndrome is a rare disease with mortality in the first year of life reported as high as 95% predominantly due to progressive heart failure from valvar regurgitation and cardiomyopathy. Multisystem involvement and uncertain prognosis have historically precluded transplant candidacy, and current management options are of limited success.

CASE REPORT

We present a baby girl with a postnatal diagnosis of neonatal Marfan syndrome who at 1 year of age underwent mitral valve and tricuspid valve repair with postoperative profound left ventricular and moderate right ventricular dysfunction necessitating biventricular assist device (BiVAD) support and subsequent heart transplant. A number of noncardiac issues persisted in our patient; however, she enjoyed a good quality of life for the initial 3 years posttransplant. Unfortunately, she subsequently developed rapidly progressive coronary allograft vasculopathy (CAV) with progressive deterioration in function and cardiac arrest.

CONCLUSION

To our best knowledge, this is only the second case of neonatal Marfan syndrome to undergo heart transplant reported in the literature and the first with BiVAD support as a bridge to candidacy. This is also the first case of neonatal Marfan syndrome associated with intragenic duplication. This case though demonstrating that earlier listing, ventricular assist device (VAD) support and even primary transplant as treatment in neonatal Marfan syndrome should all be considered viable options but also portends a cautionary tale given the spectrum of comorbidities in this rare and severe disorder.

TGFβ-2 haploinsufficiency causes early death in mice with Marfan syndrome

To assess the contribution of individual TGF-β isoforms to aortopathy in Marfan syndrome (MFS), we quantified the survival and phenotypes of mice with a combined fibrillin1 (the gene defective in MFS) hypomorphic mutation and a TGF-β1, 2, or 3 heterozygous null mutation. The loss of TGF-β2, and only TGF-β2, resulted in 80% of the double mutant animals dying earlier, by postnatal day 20, than MFS only mice. Death was not from thoracic aortic rupture, as observed in MFS mice, but was associated with hyperplastic aortic valve leaflets, aortic regurgitation, enlarged aortic root, increased heart weight, and impaired lung alveolar septation. Thus, there appears to be a relationship between loss of fibrillin1 and TGF-β2 in the postnatal development of the heart, aorta and lungs.

Thoracolumbar Scoliosis in Pediatric Patients With Loeys-Dietz Syndrome: A Case Series

Background Loeys-Dietz syndrome (LDS) is a genetic connective tissue disorder that predominantly affects cardiovascular, skeletal, and craniofacial structures. Associated thoracolumbar scoliosis in LDS can be challenging to manage, though other etiologies of pediatric scoliosis have better-defined management guidelines. We examined our institutional experience regarding the treatment of pediatric patients with LDS and scoliosis. Methodology In this retrospective study, all patients seen at our pediatric tertiary care center from 2004 through 2018 with a diagnosis of LDS were reviewed, and those with radiographic diagnoses of scoliosis (full-length scoliosis X-rays) were included. Demographic, clinical, and radiographic parameters were collected, and management strategies were reported. Results A total of 39 LDS patients whose ages ranged between seven and 13 years were identified. A total of nine patients were radiographically diagnosed with scoliosis, but three patients were excluded due to incomplete medical records, leaving six patients. The median age at scoliosis diagnosis was 11.5 years, with a median follow-up of 51 months. Two patients were successfully managed with observation (average initial Cobb angle (CA): 14°, average final CA: 20.5°). Two were braced, one successfully (initial CA: 15°, final CA: 30°) and one with a progressive disease requiring surgery (initial CA: 40°, final CA: 58°). Of the two who were offered surgical correction, one underwent surgery with a durable correction of spinal deformity (CA: 33° to 19°). One patient underwent a recent correction of aortic root dilatation and was not a candidate for scoliosis surgery. Conclusions Principles of adolescent idiopathic scoliosis management such as bracing for CA of 20-50° and surgery for CA of >50° can be applied to LDS patients with good outcomes. This augments our understanding of the treatment algorithm for pediatric patients with LDS.

Hemodynamic deterioration due to increased anterior and posterior cardiac compression during posterior spinal fusion for scoliosis with pectus excavatum

Hemodynamics may deteriorate during the perioperative period when performing posterior spinal fusion in patients with pectus excavatum and scoliosis. A 13-year-old teenager diagnosed with Marfan syndrome had thoracic scoliosis and pectus excavatum. Thoracic scoliosis was convex to the right, and a right ventricular inflow tract stenosis was observed due to compression induced by the depressed sternum. The patient underwent T3–L4 posterior spinal fusion surgery for scoliosis. Deterioration of hemodynamics was observed when the patient was placed in the prone position or when the thoracic spine was corrected to the left front. Postoperative computed tomography examination showed that the mediastinal space was narrowed due to the corrected thoracic spine. Special attention should be paid in the following cases: (1) severe pectus excavatum, (2) right ventricular inflow tract compression due to depressed sternum on the left side, (3) correction of the thoracic spine on the left front, (4) long-term surgery, and (5) risk of massive bleeding. In some cases, pectus excavatum surgery should be prioritized.

Classification and Interpretation for 11 FBN1 Variants Responsible for Marfan Syndrome and Pre-implantation Genetic Testing (PGT) for Two Families Successfully Blocked Transmission of the Pathogenic Mutations

Background: The lifespan of Marfan Syndrome (MFS) patients is shortened, especially in patients without early diagnostics, preventive treatment, and elective surgery. Clinically, MFS diagnosis is mainly dependent on phenotypes, but for children, sporadic cases, or suspicious MFS patients, molecular genetic testing, and mainly FBN1 mutation screening, plays a significant role in the diagnosis of MFS. PGT-M gives couples that had a family history of monogenic disorders the opportunity to avoid the occurrence of MFS.

Methods: In this study, 11 families with MFS were recruited and complete clinical features were collected. Variants were classified and interpreted through pedigree analysis according to guidelines. Two families chose to undergo PGT-M; 16 blastocysts were biopsied and amplified. Haplotype analysis was performed to deduce the embryo’s genotype by using single nucleotide polymorphisms (SNPs) identified in each sample.

Results: We identified 11 potential disease-causing FBN1 variants, six of which are novel. All variants were assessed with prediction tools to assess mutation pathogenicity, population databases to evaluate population allele frequency, literature databases to identify whether the variant had been reported in MFS patients, and multiple sequence alignment to carry out conservative analysis. Finally, nine variants were classified as likely pathogenic/pathogenic variants. Among 11 variants, eight variants were missense, and seven of them were located in the Ca-binding EGF-like motifs, moreover, half of them substituted conserved Cysteine residues. We also identified a splice site variant, a frameshift variant, and a synonymous variant. There are two variants that are de novo variants. PGT-M helped two MFS families give birth to a healthy baby not carrying the FBN1 mutation.

Conclusions: In the present study, the FBN1 mutation spectrum was enriched, and may help further elucidate the pathogenesis, benefiting clinical diagnosis and management of MFS. We make use of a reliable PGT-M method for the successful birth of healthy babies to two MFS families.

Exome Sequencing Identifies a Novel FBN1 Variant in a Pakistani Family with Marfan Syndrome That Includes Left Ventricle Diastolic Dysfunction

INTRODUCTION

Cardiomyopathies are diseases of the heart muscle and are important causes of heart failure. Dilated cardiomyopathy (DCM) is a common form of cardiomyopathy that can be acquired, syndromic or non-syndromic. The current study was conducted to explore the genetic defects in a Pakistani family with cardiac disease and features of Marfan's syndrome (MFS).

METHODS

A family with left ventricle (LV) diastolic dysfunction and MFS phenotype was assessed in Pakistan. The clinical information and blood samples from the patients were collected after physical, cardiovascular, and ophthalmologic examinations. An affected individual (proband) was subjected to whole-exome sequencing (WES). The findings were further validated through Sanger sequencing in the family.

RESULTS

Through WES and sanger validation, we identified a novel variant NM_000138.4; c.1402A>G in the Fibrillin-1 (FBN1) gene that segregates with LV diastolic dysfunction and MFS. Furthermore, bioinformatic evaluation suggested that the novel variant is deleterious and disease-causing.

CONCLUSIONS

This study identified for the first time a novel FBN1 variant in a family with LV diastolic dysfunction and MFS in Pakistan.

Vitamin B Mitigates Thoracic Aortic Dilation in Marfan Syndrome Mice by Restoring the Canonical TGF-β Pathway

Thoracic aortic aneurysm (TAA) formation is a multifactorial process that results in diverse clinical manifestations and drug responses. Identifying the critical factors and their functions in Marfan syndrome (MFS) pathogenesis is important for exploring personalized medicine for MFS. Methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR), and methionine synthase reductase (MTRR) polymorphisms have been correlated with TAA severity in MFS patients. However, the detailed relationship between the folate-methionine cycle and MFS pathogenesis remains unclear. Fbn1^C1039G/+ mice were reported to be a disease model of MFS. To study the role of the folate-methionine cycle in MFS, Fbn1^C1039G/+ mice were treated orally with methionine or vitamin B mixture (VITB), including vitamins B6, B9, and B12, for 20 weeks. VITB reduced the heart rate and circumference of the ascending aorta in Fbn1^C1039G/+ mice. Our data showed that the Mtr and Smad4 genes were suppressed in Fbn1^C1039G/+ mice, while VITB treatment restored the expression of these genes to normal levels. Additionally, VITB restored canonical transforming-growth factor β (TGF-β) signaling and promoted Loxl1-mediated collagen maturation in aortic media. This study provides a potential method to attenuate the pathogenesis of MFS that may have a synergistic effect with drug treatments for MFS patients.

Vascular Ehlers-Danlos Syndrome: Treatment of a Complex Abdominal Wound with Vitamin C and Mesenchymal Stromal Cells

ABSTRACT

Vascular Ehlers-Danlos syndrome (EDSv) can present with life-threatening surgical complications. The article describes the case of a patient with EDSv who developed total abdominal wound dehiscence and multiple enterocutaneous fistulas. Treatment with IV allogeneic mesenchymal stromal cells (MSCs) and high-dose vitamin C was trialed with success. Near-complete wound healing of the abdominal dehiscence with a 94% reduction in the size of the wound bed occurred. Maturation of the enterocutaneous fistulas also ensued.There is no current consensus on the management of large cutaneous wounds in EDSv. This article discusses the pathophysiology of wound healing with regard to nutrition requirements and growth factors with special reference to collagen deficits in EDSv. A potential therapy with IV vitamin C supplementation and MSCs is proposed following the patient's positive outcome. Medium-dose MSCs and high-dose IV vitamin C may offer significant benefits to complex and problematic wounds.

Potential predictors of severe cardiovascular involvement in Marfan syndrome: the emphasized role of genotype-phenotype correlations in improving risk stratification-a literature review

BACKGROUND

Marfan syndrome (MFS) is a genetically determined systemic connective tissue disorder, caused by a mutation in the FBN1 gene. In MFS mainly the cardiovascular, musculoskeletal and ocular systems are affected. The most dangerous manifestation of MFS is aortic dissection, which needs to be prevented by a prophylactic aortic root replacement.

MAIN BODY

The indication criteria for the prophylactic procedure is currently based on aortic diameter, however aortic dissections below the threshold defined in the guidelines have been reported, highlighting the need for a more accurate risk stratification system to predict the occurrence of aortic complications. The aim of this review is to present the current knowledge on the possible predictors of severe cardiovascular manifestations in MFS patients, demonstrating the wide range of molecular and radiological differences between people with MFS and healthy individuals, and more importantly between MFS patients with and without advanced aortic manifestations. These differences originating from the underlying common molecular pathological processes can be assessed by laboratory (e.g. genetic testing) and imaging techniques to serve as biomarkers of severe aortic involvement. In this review we paid special attention to the rapidly expanding field of genotype-phenotype correlations for aortic features as by collecting and presenting the ever growing number of correlations, future perspectives for risk stratification can be outlined.

CONCLUSIONS

Data on promising biomarkers of severe aortic complications of MFS have been accumulating steadily. However, more unifying studies are required to further evaluate the applicability of the discussed predictors with the aim of improving the risk stratification and therefore the life expectancy and quality of life of MFS patients.

Fracture Rates and Fracture Risk in Patients With Marfan Syndrome: A Nationwide Register-Based Cohort Study

Marfan syndrome (MFS), a rare genetic disease, has a prevalence of 6.5 in 100,000. Studies show that patients with MFS have reduced areal bone mineral density (BMD) compared with non-MFS individuals. We have previously shown that patients with MFS have reduced volumetric BMD and compromised trabecular and cortical bone microarchitecture. The present study was a registry-based, nationwide, population-based, cohort study using register data, aimed to evaluate fracture risk and fracture rates in MFS. We included 406 (196 women) patients with MFS through the Danish National Patient Register and 40,724 (19,327 women) persons, randomly selected and matched from the Civil Registry System. A total of 21.9% of the MFS and 18.9% of the reference population had experienced at least one fracture from 1995 to 2018. The fracture incidence rate was 27.5 per 1000 person-years in the MFS cohort (highest in young men and old women with MFS), and 20.3 per 1000 person-years in the reference population. The overall incidence rate ratio between the MFS and the reference population was 1.35 (95% confidence interval [CI ] 1.18-1.55) for all fractures. When evaluating the risk of being registered with an osteoporosis diagnosis in the Danish National Patient Register, starting relevant treatment for osteoporosis or experiencing a hip or spine fracture, 10.3% of the MFS cohort and 3.3% of the reference population could be classified as being osteoporotic. The between-group subhazard ratio was 3.97 (95% CI 2.56-6.25). Patients with MFS started treatment with an antiosteoporotic drug at a younger age than the reference population (57 [interquartile range 55-67] versus 71 [63-73]) years. The life expectancy in MFS is increasing, resulting in more patients facing diseases that are related to old age, such as age-related bone loss and increased risk of fractures. Our data suggest that bone health and fracture prevention needs to be part of the standard care for patients with MFS. © 2021 American Society for Bone and Mineral Research (ASBMR).

Reversion-inducing cysteine-rich protein with Kazal motifs and MT1-MMP promote the formation of robust fibrillin fibers

Fibrillins (FBNs) form mesh-like structures of microfibrils in various elastic tissues. RECK and FBN1 are co-expressed in many human tissues, suggesting a functional relationship. We found that dermal FBN1 fibers show atypical morphology in mice with reduced RECK expression (RECK-Hypo mice). Dermal FBN1 fibers in mice-lacking membrane-type 1-matrix metalloproteinase (MT1-MMP) show a similar atypical morphology, despite the current notion that MT1-MMP (a membrane-bound protease) and RECK (a membrane-bound protease inhibitor) have opposing functions. Our experiments using dermal fibroblasts indicated that RECK promotes pro-MT1-MMP activation, increases cell-associated gelatinase/collagenase activity, and decreases diffusible gelatinase/collagenase activity, while MT1-MMP stabilizes RECK in these cells. Experiments using purified proteins indicate that RECK and its binding partner ADAMTS10 keep the proteolytic activity of MT1-MMP within a certain range. These findings suggest that RECK, ADAMTS10, and MT1-MMP cooperate to support the formation of robust FBN1 fibers.

The Collagens DPY-17 and SQT-3 Direct Anterior-Posterior Migration of the Q Neuroblasts in C. elegans

Cell adhesion molecules and their extracellular ligands control morphogenetic events such as directed cell migration. The migration of neuroblasts and neural crest cells establishes the structure of the central and peripheral nervous systems. In C. elegans, the bilateral Q neuroblasts and their descendants undergo long-range migrations with left/right asymmetry. QR and its descendants on the right migrate anteriorly, and QL and its descendants on the left migrate posteriorly, despite identical patterns of cell division, cell death, and neuronal generation. The initial direction of protrusion of the Q cells relies on the left/right asymmetric functions of the transmembrane receptors UNC-40/DCC and PTP-3/LAR in the Q cells. Here, we show that Q cell left/right asymmetry of migration is independent of the GPA-16/Gα pathway which regulates other left/right asymmetries, including nervous system L/R asymmetry. No extracellular cue has been identified that guides initial Q anterior versus posterior migrations. We show that collagens DPY-17 and SQT-3 control initial Q direction of protrusion. Genetic interactions with UNC-40/DCC and PTP-3/LAR suggest that DPY-17 and SQT-3 drive posterior migration and might act with both receptors or in a parallel pathway. Analysis of mutants in other collagens and extracellular matrix components indicated that general perturbation of collagens and the extracellular matrix (ECM) did not result in directional defects, and that the effect of DPY-17 and SQT-3 on Q direction is specific. DPY-17 and SQT-3 are components of the cuticle, but a role in the basement membrane cannot be excluded. Possibly, DPY-17 and SQT-3 are part of a pattern in the cuticle and/or basement membrane that is oriented to the anterior–posterior axis of the animal and that is deciphered by the Q cells in a left–right asymmetric fashion. Alternatively, DPY-17 and SQT-3 might be involved in the production or stabilization of a guidance cue that directs Q migrations. In any case, these results describe a novel role for the DPY-17 and SQT-3 collagens in directing posterior Q neuroblast migration.

Bone Geometry, Density, and Microarchitecture in the Distal Radius and Tibia in Adults With Marfan Syndrome Assessed by HR-pQCT

Marfan syndrome (MFS) is a hereditary disorder of connective tissue caused by mutations in the fibrillin-1 gene. Studies have shown that patients with MFS have lower bone mass, but little is known about the other constituents of bone strength. We hypothesize that patients with MFS will have larger bone area and compromised cortical microarchitecture compared with non-MFS individuals. A total of 74 adult patients with MFS and 145 age- and sex-matched non-MFS reference individuals were included in this study. High-resolution peripheral quantitative computed tomography (HR-pQCT) at the distal radius and distal tibia and dual-energy X-ray absorptiometry of total hip and the lumbar spine were performed, and bone turnover and sex hormones were measured. Patients with MFS had significantly lower areal bone mineral density (BMD) at the total spine (-13%) and total hip (-7%) when compared with the reference group. Patients with MFS had significantly larger total bone area at both the radius (+27%) and tibia (+34%). Volumetric BMD at both measured sites showed significantly reduced total, trabecular, and cortical volumetric BMD in patients with MFS compared with the reference group. The microarchitectural parameters at the radius and tibia were compromised in patients with MFS with significantly reduced trabecular number and thickness, leading to a higher trabecular separation and significantly reduced cortical thickness and increased cortical porosity compared with the reference group. The differences in bone density, geometry, or microarchitecture were not explained by increased bone turnover markers or circulating levels of sex hormones. We conclude patients with MFS have altered bone geometry, altered bone microstructure, and lower bone mass (lower areal BMD and volumetric BMD at all sites) compared with healthy reference individuals. Future studies should focus on fracture rates and fracture risk in adult and aging patients with MFS. © 2020 American Society for Bone and Mineral Research (ASBMR).

Progress and challenges in CRISPR-mediated therapeutic genome editing for monogenic diseases

There are an estimated 10 000 monogenic diseases affecting tens of millions of individuals worldwide. The application of CRISPR/Cas genome editing tools to treat monogenic diseases is an emerging strategy with the potential to generate personalized treatment approaches for these patients. CRISPR/Cas-based systems are programmable and sequence-specific genome editing tools with the capacity to generate base pair resolution manipulations to DNA or RNA. The complexity of genomic insults resulting in heritable disease requires patient-specific genome editing strategies with consideration of DNA repair pathways, and CRISPR/Cas systems of different types, species, and those with additional enzymatic capacity and/or delivery methods. In this review we aim to discuss broad and multifaceted therapeutic applications of CRISPR/Cas gene editing systems including in harnessing of homology directed repair, non-homologous end joining, microhomology-mediated end joining, and base editing to permanently correct diverse monogenic diseases.

Overexpression of TGF-β1 induces renal fibrosis and accelerates the decline in kidney function in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the presence of numerous fluid-filled cysts, extensive fibrosis, and the progressive decline in kidney function. Transforming growth factor-β1 (TGF-β1), an important mediator for renal fibrosis and chronic kidney disease, is overexpressed by cystic cells compared with normal kidney cells; however, its role in PKD pathogenesis remains undefined. To investigate the effect of TGF-β1 on cyst growth, fibrosis, and disease progression, we overexpressed active TGF-β1 specifically in collecting ducts (CDs) of phenotypic normal (Pkd1^RC/+) and Pkd1^RC/RC mice. In normal mice, CD-specific TGF-β1 overexpression caused tubule dilations by 5 wk of age that were accompanied by increased levels of phosphorylated SMAD3, α-smooth muscle actin, vimentin, and periostin; however, it did not induce overt cyst formation by 20 wk. In Pkd1^RC/RC mice, CD overexpression of TGF-β1 increased cyst epithelial cell proliferation. However, extensive fibrosis limited cyst enlargement and caused contraction of the kidneys, leading to a loss of renal function and a shortened lifespan of the mice. These data demonstrate that TGF-β1-induced fibrosis constrains cyst growth and kidney enlargement and accelerates the decline of renal function, supporting the hypothesis that a combined therapy that inhibits renal cyst growth and fibrosis will be required to effectively treat ADPKD.

The fibrillin microfibril/elastic fibre network: A critical extracellular supramolecular scaffold to balance skin homoeostasis

Supramolecular networks composed of fibrillins (fibrillin-1 and fibrillin-2) and associated ligands form intricate cellular microenvironments which balance skin homoeostasis and direct remodelling. Fibrillins assemble into microfibrils which are not only indispensable for conferring elasticity to the skin, but also control the bioavailability of growth factors targeted to the extracellular matrix architecture. Fibrillin microfibrils (FMF) represent the core scaffolds for elastic fibre formation, and they also decorate the surface of elastic fibres and form independent networks. In normal dermis, elastic fibres are suspended in a three-dimensional basket-like lattice of FMF intersecting basement membranes at the dermal-epidermal junction and thus conferring pliability to the skin. The importance of FMF for skin homoeostasis is illustrated by the clinical features caused by mutations in the human fibrillin genes (FBN1, FBN2), summarized as "fibrillinopathies." In skin, fibrillin mutations result in phenotypes ranging from thick, stiff and fibrotic skin to thin, lax and hyperextensible skin. The most plausible explanation for this spectrum of phenotypic outcomes is that FMF regulate growth factor signalling essential for proper growth and homoeostasis of the skin. Here, we will give an overview about the current understanding of the underlying pathomechanisms leading to fibrillin-dependent fibrosis as well as forms of cutis laxa caused by mutational inactivation of FMF-associated ligands.

Acromelic dysplasias: how rare musculoskeletal disorders reveal biological functions of extracellular matrix proteins

Acromelic dysplasias are a group of rare musculoskeletal disorders that collectively present with short stature, pseudomuscular build, stiff joints, and tight skin. Acromelic dysplasias are caused by mutations in genes (FBN1, ADAMTSL2, ADAMTS10, ADAMTS17, LTBP2, and LTBP3) that encode secreted extracellular matrix proteins, and in SMAD4, an intracellular coregulator of transforming growth factor-β (TGF-β) signaling. The shared musculoskeletal presentations in acromelic dysplasias suggest that these proteins cooperate in a biological pathway, but also fulfill distinct roles in specific tissues that are affected in individual disorders of the acromelic dysplasia group. In addition, most of the affected proteins directly interact with fibrillin microfibrils in the extracellular matrix and have been linked to the regulation of TGF-β signaling. Together with recently developed knockout mouse models targeting the affected genes, novel insights into molecular mechanisms of how these proteins regulate musculoskeletal development and homeostasis have emerged. Here, we summarize the current knowledge highlighting pathogenic mechanisms of the different disorders that compose acromelic dysplasias and provide an overview of the emerging biological roles of the individual proteins that are compromised. Finally, we develop a conceptual model of how these proteins may interact and form an "acromelic dysplasia complex" on fibrillin microfibrils in connective tissues of the musculoskeletal system.

Normal Ranges of Upper Extremity Length, Circumference, and Rate of Growth in the Pediatric Population

Background: Upper extremity length and circumference abnormalities are present in a number of conditions in the pediatric population. In most cases, upper limb hypoplasia and hypertrophy are diagnosed when one limb appears substantially different from the other during physical examination. However, occasionally when this discrepancy exists, it can be difficult to determine which limb is the abnormal one. The purpose of this study was to establish normal values for upper extremity length, circumference, and rate of growth in children aged 0 to 17 years. Methods: In all, 377 participants had 4 measurements taken of each upper extremity: upper arm length, upper arm circumference, forearm length, and forearm circumference. Statistical analysis was performed to identify differences and rates of growth. Results: Mean values for arm and forearm length and circumference for each age, 0 to 17 years, were established. The determination of a child's expected arm length is dependent on his or her height, age, and sex, while the calculation of a child's expected forearm length depends on his or her weight, age, and sex. Male and female arms and forearms have similar growth rates of lengths and circumferences. No significant differences were found between right and left extremities for each of the 4 measurements taken. Conclusions: Contralateral limbs can be used for comparison of length and circumference of the arm and forearm in cases of unilateral upper extremity abnormality. The establishment of normal values for upper extremity length, circumference, and growth rate will be a useful diagnostic tool for upper extremity hypoplasia and hypertrophy.

Is HSPG2 a modifier gene for Marfan syndrome?

Marfan syndrome (MFS) is a connective tissue disease caused by variants in the FBN1 gene. Nevertheless, other genes influence the manifestations of the disease, characterized by high clinical variability even within families. We mapped modifier loci for cardiovascular and skeletal manifestations in the mg∆loxPneo mouse model for MFS and the synthenic loci in the human genome. Corroborating our findings, one of those loci was identified also as a modifier locus in MFS patients. Here, we investigate the HSPG2 gene, located in this region, as a candidate modifier gene for MFS. We show a correlation between Fbn1 and Hspg2 expression in spinal column and aorta in non-isogenic mg∆loxPneo mice. Moreover, we show that mice with severe phenotypes present lower expression of Hspg2 than those mildly affected. Thus, we propose that HSPG2 is a strong candidate modifier gene for MFS and its role in modulating disease severity should be investigated in patients.

Marfan syndrome revisited: From genetics to the clinic

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

Generation of a human induced pluripotent stem cell line (NCCDFWi001-A) from a Marfan syndrome patient carrying two FBN1 variants (c.2613A > C and c.684_736 + 4del)

The human induced pluripotent stem cell line NCCDFWi001-A was derived from peripheral blood mononuclear cells (PBMC) of a 26-year-old female Marfan syndrome patient carrying two compound heterozygous variants FBN1c.2613A > C, (p.Leu871Phe) and c.684_736 + 4del. The established patient-derived iPSC showed expression of pluripotent stem cell markers and had the ability to differentiate into all of the three germ layers and possessed a normal karyotype.

Therapies for Thoracic Aortic Aneurysms and Acute Aortic Dissections

Thoracic aortic aneurysms that progress to acute aortic dissections are often fatal. Thoracic aneurysms have been managed with treatment with β-adrenergic blocking agents (β-blockers) and routine surveillance imaging, followed by surgical repair of the aneurysm when the risk of dissection exceeds the risk for repair. Thus, there is a window to initiate therapies to slow aortic enlargement and delay or ideally negate the need for surgical repair of the aneurysm to prevent a dissection. Mouse models of Marfan syndrome-a monogenic disorder predisposing to thoracic aortic disease-have been used extensively to identify such therapies. The initial finding that TGFβ (transformation growth factor-β) signaling was increased in the aortic media of a Marfan syndrome mouse model and that its inhibition via TGFβ neutralization or At1r (Ang II [angiotensin II] type I receptor) antagonism prevented aneurysm development was generally viewed as a groundbreaking discovery that could be translated into the first cure of thoracic aortic disease. However, several large randomized trials of pediatric and adult patients with Marfan syndrome have subsequently yielded no evidence that At1r antagonism by losartan slows aortic enlargement more effectively than conventional treatment with β-blockers. Subsequent studies in mouse models have begun to resolve the complex molecular pathophysiology underlying onset and progression of aortic disease and have emphasized the need to preserve TGFβ signaling to prevent aneurysm formation. This review describes critical experiments that have influenced the evolution of our understanding of thoracic aortic disease, in addition to discussing old controversies and identifying new therapeutic opportunities.

Arteriopathy of Unknown Etiology: Pathologic, Radiologic, and Cytogenetic Investigations

Patient: Male, 38

Final Diagnosis: Arteriopathy of unknown etiology

Symptoms: Left groin pain

Medication: —

Clinical Procedure: —

Specialty: Neurology

Visual outcome and surgical results in children with Marfan syndrome

IMPORTANCE

To determine visual and surgical results in children with Marfan syndrome.

BACKGROUND

Marfan syndrome involves ocular complications which can lead to visual disturbance and amblyopia. Data about the visual and surgical results in children with Marfan syndrome is vital for the clinical management of these patients.

DESIGN

Retrospective data analysis.

PARTICIPANTS

Eighty-two eyes of 41 patients with a genetically proved diagnosis of Marfan syndrome.

METHODS

Medical records of patients with Marfan syndrome were reviewed between 2007 and 2017. Ocular complications, visual acuity (VA) of patients with/without lensectomy and surgical method were evaluated.

MAIN OUTCOME MEASURES

VA outcomes of patients with Marfan syndrome with/without surgical repair of ectopia lentis.

RESULTS

In 27 (66%) of the 41 patients a bilateral subluxation of the lens was visible and 14 (52%) patients received lensectomy. The mean age at initial presentation was 12.3 ± 9 years and mean follow-up was 3 years (range 1-7). VA varied from 1.2 to -0.1 logMAR at first examination. At initial presentation, mean VA was 0.1 ± 0.7 logMAR in patients with a normal lens status (n = 14) and 0.3 ± 0.5 logMAR in patients with subluxation of the lens (n = 27) (P < .01). VA improved from 0.2 ± 0.5 logMAR to 0.1 ± 0.5 logMAR (P = .06) in children with subluxation of the lens who did not need a lensectomy (n = 12) and from 0.5 ± 0.5 logMAR to 0.2 ± 0.5 logMAR (P = .02) in patients who were referred to lensectomy with/without secondary lens implantation.

CONCLUSIONS AND RELEVANCE

In Marfan syndrome subluxation of the lens was found in the majority of children. Improvement of VA resulted in children with subluxation of the lens and following lensectomy.

From genetics to response to injury: vascular smooth muscle cells in aneurysms and dissections of the ascending aorta

Vascular smooth muscle cells (vSMCs) play a crucial role in both the pathogenesis of Aneurysms and Dissections of the ascending thoracic aorta (TAAD) in humans and in the associated adaptive compensatory responses, since thrombosis and inflammatory processes are absent in the majority of cases. Aneurysms and dissections share numerous characteristics, including aetiologies and histopathological alterations: vSMC disappearance, medial areas of mucoid degeneration, and extracellular matrix (ECM) breakdown. Three aetiologies predominate in TAAD in humans: (i) genetic causes in heritable familial forms, (ii) an association with bicuspid aortic valves, and (iii) a sporadic degenerative form linked to the aortic aging process. Genetic forms include mutations in vSMC genes encoding for molecules of the ECM or the TGF-β pathways, or participating in vSMC tone. On the other hand, aneurysms and dissections, whatever their aetiologies, are characterized by an increase in wall permeability leading to transmural advection of plasma proteins which could interact with vSMCs and ECM components. In this context, blood-borne plasminogen appears to play an important role, because its outward convection through the wall is increased in TAAD, and it could be converted to active plasmin at the vSMC membrane. Active plasmin can induce vSMC disappearance, proteolysis of adhesive proteins, activation of MMPs and release of TGF-β from its ECM storage sites. Conversely, vSMCs could respond to aneurysmal biomechanical and proteolytic injury by an epigenetic phenotypic switch, including constitutional overexpression and nuclear translocation of Smad2 and an increase in antiprotease and ECM protein synthesis. In contrast, such an epigenetic phenomenon is not observed in dissections. In this context, dysfunction of proteins involved in vSMC tone are interesting to study, particularly in interaction with plasma protein transport through the wall and TGF-β activation, to establish the relationship between these dysfunctions and ECM proteolysis.

A novel mutation in FBN1 gene in autosomal dominant Marfan syndrome and macular degeneration in a Chinese consanguineous family

AIM

To report a novel mutation in FBN1 gene in a Chinese consanguineous family with common Marfan syndrome (MFS) phenotype and an unusual bilateral macular degeneration.

METHODS

Ophthalmic, cardiovascular and systemic examinations were performed, and genomic DNA extracted from all living family members. The 24-32 exon mutations of FBN1 gene were screened by Sanger Sequencing in all family members and 100 unrelated healthy Chinese individuals.

RESULTS

In the four-generation family, classic MFS phenotypes were observed in all 5 patients, 2 of them had peculiar phenotype of bilateral macular degeneration. Mutation screening in FBN1 identified a heterozygous missense mutation (c.3932A>G, p.Y1311C) with co-segregation. This mutation was found with the MFS phenotypes in all 5 patients but not in unaffected members or unrelated controls.

CONCLUSION

A Chinese consanguineous MFS family with uncommon bilateral macular degeneration and an unreported c.3932A>G mutation in FBN1 was identified. Our finding expands the FBN1 mutation spectrum and its possible role in the pathogenesis of Marfan syndrome.

Adamts10 inactivation in mice leads to persistence of ocular microfibrils subsequent to reduced fibrillin-2 cleavage

Mutations in the secreted metalloproteinase ADAMTS10 cause recessive Weill-Marchesani syndrome (WMS), comprising ectopia lentis, short stature, brachydactyly, thick skin and cardiac valve anomalies. Dominant WMS caused by FBN1 mutations is clinically similar and affects fibrillin-1 microfibrils, which are a major component of the ocular zonule. ADAMTS10 was previously shown to enhance fibrillin-1 assembly in vitro. Here, Adamts10 null mice were analyzed to determine the impact of ADAMTS10 deficiency on fibrillin microfibrils in vivo. An intragenic lacZ reporter identified widespread Adamts10 expression in the eye, musculoskeletal tissues, vasculature, skin and lung. Adamts10^-/- mice had reduced viability on the C57BL/6 background, and although surviving mice were slightly smaller and had stiff skin, they lacked brachydactyly and cardiovascular defects. Ectopia lentis was not observed in Adamts10^-/- mice, similar to Fbn1^-/- mice, most likely because the mouse zonule contains fibrillin-2 in addition to fibrillin-1. Unexpectedly, in contrast to wild-type eyes, Adamts10^-/- zonule fibers were thicker and immunostained strongly with fibrillin-2 antibodies into adulthood, whereas fibrillin-1 staining was reduced. Furthermore, fibrillin-2 staining of hyaloid vasculature remnants persisted post-natally in Adamts10^-/- eyes. ADAMTS10 was found to cleave fibrillin-2, providing an explanation for persistence of fibrillin-2 at these sites. Thus, analysis of Adamts10^-/- mice led to identification of fibrillin-2 as a novel ADAMTS10 substrate and defined a proteolytic mechanism for clearance of ocular fibrillin-2 at the end of the juvenile period.

Effect of the Antioxidant Lipoic Acid in Aortic Phenotype in a Marfan Syndrome Mouse Model

Marfan syndrome (MFS) cardiovascular manifestations such as aortic aneurysms and cardiomyopathy carry substantial morbidity/mortality. We investigated the effects of lipoic acid, an antioxidant, on ROS production and aortic remodeling in a MFS mgΔ^loxPneo mouse model. MFS and WT (wild-type) 1-month-old mice were allocated to 3 groups: untreated, treated with losartan, and treated with lipoic acid. At 6 months old, echocardiography, ROS production, and morphological analysis of aortas were performed. Aortic ROS generation in 6-month-old MFS animals was higher at advanced stages of disease in MFS. An unprecedented finding in MFS mice analyzed by OCT was the occurrence of focal inhomogeneous regions in the aortic arch, either collagen-rich extremely thickened or collagen-poor hypotrophic regions. MFS animals treated with lipoic acid showed markedly reduced ROS production and lower ERK1/2 phosphorylation; meanwhile, aortic dilation and elastic fiber breakdown were unaltered. Of note, lipoic acid treatment associated with the absence of focal inhomogeneous regions in MFS animals. Losartan reduced aortic dilation and elastic fiber breakdown despite no change in ROS generation. In conclusion, oxidant generation by itself seems neutral with respect to aneurysm progression in MFS; however, lipoic acid-mediated reduction of inhomogeneous regions may potentially associate with less anisotropy and reduced chance of dissection/rupture.

TGF-β Signaling in Control of Cardiovascular Function

Genetic studies in animals and humans indicate that gene mutations that functionally perturb transforming growth factor β (TGF-β) signaling are linked to specific hereditary vascular syndromes, including Osler-Rendu-Weber disease or hereditary hemorrhagic telangiectasia and Marfan syndrome. Disturbed TGF-β signaling can also cause nonhereditary disorders like atherosclerosis and cardiac fibrosis. Accordingly, cell culture studies using endothelial cells or smooth muscle cells (SMCs), cultured alone or together in two- or three-dimensional cell culture assays, on plastic or embedded in matrix, have shown that TGF-β has a pivotal effect on endothelial and SMC proliferation, differentiation, migration, tube formation, and sprouting. Moreover, TGF-β can stimulate endothelial-to-mesenchymal transition, a process shown to be of key importance in heart valve cushion formation and in various pathological vascular processes. Here, we discuss the roles of TGF-β in vasculogenesis, angiogenesis, and lymphangiogenesis and the deregulation of TGF-β signaling in cardiovascular diseases.

Structural and functional failure of fibrillin‑1 in human diseases (Review)

Fibrillins (FBNs) are key relay molecules that form the backbone of microfibrils in elastic and non‑elastic tissues. Interacting with other components of the extracellular matrix (ECM), these ubiquitous glycoproteins exert pivotal roles in tissue development, homeostasis and repair. In addition to mechanical support, FBN networks also exhibit regulatory activities on growth factor signalling, ECM formation, cell behaviour and the immune response. Consequently, mutations affecting the structure, assembly and stability of FBN microfibrils have been associated with impaired biomechanical tissue properties, altered cell‑matrix interactions, uncontrolled growth factor or cytokine activation, and the development of fibrillinopathies and associated severe complications in multiple organs. Beyond a panoramic overview of structural cues of the FBN network, the present review will also describe the pathological implications of FBN disorders in the development of inflammatory and fibrotic conditions.

Pharmacogenetic approach to losartan in Marfan patients: a starting point to improve dosing regimen?

BACKGROUND

Losartan is under evaluation for managing Marfan patients with aortic root dilatation. Cytochrome P450 (CYP) enzymes convert losartan to E3174 active metabolite. The aim of this study is to describe the distribution of CYP2C9*2, CYP2C9*3, CYP3A4*22 and CYP3A5*3 defective alleles, according to losartan tolerance in paediatric Marfan patients.

METHODS

We genotyped 53 paediatric Marfan patients treated with losartan. The rate of aortic root dilatation was evaluated using the delta z-score variation. Differences in tolerated losartan daily doses with respect to CYP metabolic classes were assessed through the Kruskal-Wallis test.

RESULTS

The losartan daily dose spans from 0.16 to 2.50 mg/kg (median 1.10 mg/kg). As we expect from the pharmacokinetics pathway, we observe highest tolerated dose in CYP2C9 poor metabolisers (median 1.50 mg/kg, interquartile range 1.08-1.67 mg/kg); however, this difference is not statistically significant.

CONCLUSIONS

The optimal dose of angiotensin receptor blocker is not known, and no data are available about losartan pharmacogenetic profile in Marfan syndrome; we have proposed a strategy to tackle this issue based on evaluating the major genetic polymorphisms involved in the losartan conversion into active carboxylic acid metabolite. Further studies are needed to support the use of genetic polymorphisms as predictors of the right dose of losartan.

Enlarged Dural Sac in Idiopathic Bronchiectasis Implicates Heritable Connective Tissue Gene Variants

RATIONALE

Patients with idiopathic bronchiectasis are predominantly female and have an asthenic body morphotype and frequent nontuberculous mycobacterial respiratory infections. They also demonstrate phenotypic features (scoliosis, pectus deformity, mitral valve prolapse) that are commonly seen in individuals with heritable connective tissue disorders.

OBJECTIVES

To determine whether lumbar dural sac size is increased in patients with idiopathic bronchiectasis as compared with control subjects, and to assess whether dural sac size is correlated with phenotypic characteristics seen in individuals with heritable connective tissue disorders.

METHODS

Two readers blinded to diagnosis measured anterior-posterior and transverse dural sac diameter using L1-L5 magnetic resonance images of 71 patients with idiopathic bronchiectasis, 72 control subjects without lung disease, 29 patients with cystic fibrosis, and 24 patients with Marfan syndrome. We compared groups by pairwise analysis of means, using Tukey's method to adjust for multiple comparisons. Dural sac diameter association with phenotypic and clinical features was also tested.

MEASUREMENTS AND MAIN RESULTS

The L1-L5 (average) anterior-posterior dural sac diameter of the idiopathic bronchiectasis group was larger than those of the control group (P < 0.001) and the cystic fibrosis group (P = 0.002). There was a strong correlation between increased dural sac size and the presence of pulmonary nontuberculous mycobacterial infection (P = 0.007) and long fingers (P = 0.003). A trend toward larger dural sac diameter was seen in those with scoliosis (P = 0.130) and those with a family history of idiopathic bronchiectasis (P = 0.149).

CONCLUSIONS

Individuals with idiopathic bronchiectasis have an enlarged dural sac diameter, which is associated with pulmonary nontuberculous mycobacterial infection, long fingers, and family history of idiopathic bronchiectasis. These findings support our hypothesis that "idiopathic" bronchiectasis development reflects complex genetic variation in heritable connective tissue and associated transforming growth factor-β-related pathway genes.

Fell-Muir Lecture: Fibrillin microfibrils: structural tensometers of elastic tissues?

Fibrillin microfibrils are indispensable structural elements of connective tissues in multicellular organisms from early metazoans to humans. They have an extensible periodic beaded organization, and support dynamic tissues such as ciliary zonules that suspend the lens. In tissues that express elastin, including blood vessels, skin and lungs, microfibrils support elastin deposition and shape the functional architecture of elastic fibres. The vital contribution of microfibrils to tissue form and function is underscored by the heritable fibrillinopathies, especially Marfan syndrome with severe elastic, ocular and skeletal tissue defects. Research since the early 1990s has advanced our knowledge of biology of microfibrils, yet understanding of their mechanical and homeostatic contributions to tissues remains far from complete. This review is a personal reflection on key insights, and puts forward the conceptual hypothesis that microfibrils are structural 'tensometers' that direct cells to monitor and respond to altered tissue mechanics.

The Structural Role of Elastic Fibers in the Cornea Investigated Using a Mouse Model for Marfan Syndrome

Purpose

The presence of fibrillin-rich elastic fibers in the cornea has been overlooked in recent years. The aim of the current study was to elucidate their functional role using a mouse model for Marfan syndrome, defective in fibrillin-1, the major structural component of the microfibril bundles that constitute most of the elastic fibers.

Methods

Mouse corneas were obtained from animals with a heterozygous fibrillin-1 mutation (Fbn1+/-) and compared to wild type controls. Corneal thickness and radius of curvature were calculated using optical coherence tomography microscopy. Elastic microfibril bundles were quantified and visualized in three-dimensions using serial block face scanning electron microscopy. Transmission electron microscopy was used to analyze stromal ultrastructure and proteoglycan distribution. Center-to-center average interfibrillar spacing was determined using x-ray scattering.

Results

Fbn1+/- corneas were significantly thinner than wild types and displayed a higher radius of curvature. In the Fbn1+/- corneas, elastic microfibril bundles were significantly reduced in density and disorganized compared to wild-type controls, in addition to containing a higher average center-to-center collagen interfibrillar spacing in the center of the cornea. No other differences were detected in stromal ultrastructure or proteoglycan distribution between the two groups. Proteoglycan side chains appeared to colocalize with the microfibril bundles.

Conclusions

Elastic fibers have an important, multifunctional role in the cornea as highlighted by the differences observed between Fbn1+/- and wild type animals. We contend that the presence of normal quantities of structurally organized elastic fibers are required to maintain the correct geometry of the cornea, which is disrupted in Marfan syndrome.

The role of advanced echocardiography and cardiovascular magnetic resonance in the assessment of myocardial function in Marfan syndrome-An update

Cardiovascular assessment of patients with Marfan syndrome has normally focused on the aortic root and vascular manifestations of the disease due to the high risk of aortic dissection. Although primary myocardial impairment has long been suspected in these patients, the evidence has been controversial. Advanced echocardiography and cardiovascular magnetic resonance imaging have proven to be effective, accurate, and more sensitive in the detection of subtle cardiac dysfunction. The application of these techniques to Marfan syndrome over the last 10 years has made significant progress in demonstrating the presence of primary myocardial impairment in these patients, but further work is still required to obtain confirmatory molecular, pathophysiological, and prognostic clinical data. Phenotypic expression of the disease has prognostic value, also suggesting potential effective medical therapy.

Latent TGF-β binding protein 2 and 4 have essential overlapping functions in microfibril development

Microfibrils are exracellular matrix components necessary for elastic fiber assembly and for suspending lenses. We previously reported that latent TGF-β binding protein 2 (LTBP-2), a microfibril-associated protein, is required for forming stable microfibril bundles in ciliary zonules. However, it was not understood why Ltbp2 null mice only showed an eye-specific phenotype, whereas LTBP-2 is abundantly expressed in other tissues containing microfibrils in wild type mice. Here, we show that LTBP-4, another microfibril-associated protein, compensates for the loss of LTBP-2 in microfibril formation. Ltbp2/4S double knockout (DKO) mice showed increased lethality due to emphysema, which was much more severe than that found in Ltbp4S null mice. Elastic fibers in the lungs of Ltbp2/4S DKO mice were severely disorganized and fragmented. Cultured mouse embryonic fibroblasts (MEFs) from Ltbp2/4S DKO embryos developed reduced microfibril meshwork in serum-free conditions, whereas the microfibril formation was restored by the addition of either recombinant LTBP-2 or -4. Finally, ectopic expression of LTBP-4 in the whole body restored ciliary zonule microfibril bundles in the eyes of Ltbp2 null mice. These data suggest that LTBP-2 and -4 have critical overlapping functions in forming the robust structure of microfibrils in vitro and in vivo.

An iPSC-derived vascular model of Marfan syndrome identifies key mediators of smooth muscle cell death

Marfan syndrome (MFS) is a heritable connective tissue disorder caused by mutations in FBN1, which encodes the extracellular matrix protein fibrillin-1. To investigate the pathogenesis of aortic aneurysms in MFS, we generated a vascular model derived from human induced pluripotent stem cells (MFS-hiPSCs). Our MFS-hiPSC-derived smooth muscle cells (SMCs) recapitulated the pathology seen in Marfan aortas, including defects in fibrillin-1 accumulation, extracellular matrix degradation, transforming growth factor-β (TGF-β) signaling, contraction and apoptosis; abnormalities were corrected by CRISPR-based editing of the FBN1 mutation. TGF-β inhibition rescued abnormalities in fibrillin-1 accumulation and matrix metalloproteinase expression. However, only the noncanonical p38 pathway regulated SMC apoptosis, a pathological mechanism also governed by Krüppel-like factor 4 (KLF4). This model has enabled us to dissect the molecular mechanisms of MFS, identify novel targets for treatment (such as p38 and KLF4) and provided an innovative human platform for the testing of new drugs.

Characterization of pain, disability, and psychological burden in Marfan syndrome

The clinical manifestations of Marfan syndrome frequently cause pain. This study aimed to characterize pain in a cohort of adults with Marfan syndrome and investigate demographic, physical, and psychological factors associated with pain and pain-related disability. Two hundred and forty-five participants (73% female, 89% non-Hispanic white, 90% North American) completed an online questionnaire assessing clinical features of Marfan syndrome, pain severity, pain-related disability, physical and mental health, depressive symptoms, pain catastrophizing, and insomnia. Eighty-nine percent of respondents reported having pain with 28% of individuals reporting pain as a presenting symptom of Marfan syndrome. Almost half of individuals reported that pain has spread from its initial site. Participants in our study reported poor physical and mental health functioning, moderate pain-related disability, and mild levels of depressive symptoms, sleep disturbances, and pain catastrophizing. Those who identified pain as an initial symptom of Marfan syndrome and those who reported that pain had spread from its initial site reported greater psychological burden compared with those without pain as an initial symptom or pain spreading. Physical health is the largest predictor of pain severity and pain-related disability. While pain catastrophizing and worse mental health functioning are significant correlates of pain severity and pain-related disability, respectively. Pain is a significant and persistent problem in Marfan syndrome and is associated with profound disability and psychological burden. Further studies are indicated to better characterize the directionality of pain, pain-related disability, and psychological burden in Marfan syndrome. © 2016 Wiley Periodicals, Inc.

The TGF-β Signalling Network in Muscle Development, Adaptation and Disease

Skeletal muscle possesses remarkable ability to change its size and force-producing capacity in response to physiological stimuli. Impairment of the cellular processes that govern these attributes also affects muscle mass and function in pathological conditions. Myostatin, a member of the TGF-β family, has been identified as a key regulator of muscle development, and adaptation in adulthood. In muscle, myostatin binds to its type I (ALK4/5) and type II (ActRIIA/B) receptors to initiate Smad2/3 signalling and the regulation of target genes that co-ordinate the balance between protein synthesis and degradation. Interestingly, evidence is emerging that other TGF-β proteins act in concert with myostatin to regulate the growth and remodelling of skeletal muscle. Consequently, dysregulation of TGF-β proteins and their associated signalling components is increasingly being implicated in muscle wasting associated with chronic illness, ageing, and inactivity. The growing understanding of TGF-β biology in muscle, and its potential to advance the development of therapeutics for muscle-related conditions is reviewed here.

Marfan syndrome: current perspectives

Marfan syndrome (MFS) is a pleiotropic connective tissue disease inherited as an autosomal dominant trait, due to mutations in the FBN1 gene encoding fibrillin 1. It is an important protein of the extracellular matrix that contributes to the final structure of a microfibril. Few cases displaying an autosomal recessive transmission are reported in the world. The FBN1 gene, which is made of 66 exons, is located on chromosome 15q21.1. This review, after an introduction on the clinical manifestations that leads to the diagnosis of MFS, focuses on cardiovascular manifestations, pharmacological and surgical therapies of thoracic aortic aneurysm and/or dissection (TAAD), mechanisms underlying the progression of aneurysm or of acute dissection, and biomarkers associated with progression of TAADs. A Dutch group compared treatment with losartan, an angiotensin II receptor-1 blocker, vs no other additional treatment (COMPARE clinical trial). They observed that losartan reduces the aortic dilatation rate in patients with Marfan syndrome. Later on, they also reported that losartan exerts a beneficial effect on patients with Marfan syndrome carrying an FBN1 mutation that causes haploinsufficiency (quantitative mutation), while it has no significant effect on patients displaying dominant negative (qualitative) mutations. Moreover, a French group in a 3-year trial compared the administration of losartan vs placebo in patients with Marfan syndrome under treatment with beta-receptor blockers. They observed that losartan decreases blood pressure but has no effect on aortic diameter progression. Thus, beta-receptor blockers remain the gold standard therapy in patients with Marfan syndrome. Three potential biochemical markers are mentioned in this review: total homocysteine, serum transforming growth factor beta, and lysyl oxidase. Moreover, markers of oxidative stress measured in plasma, previously correlated with clinical features of Marfan syndrome, may be explored as potential biomarkers of clinical severity.

Fibrillin-1 microfibrils influence adult bone marrow hematopoiesis

We have recently demonstrated that fibrillin-1 assemblies regulate the fate of skeletal stem cells (aka, mesenchymal stem cells [MSCs]) by modulating TGFβ activity within the microenvironment of adult bone marrow niches. Since MSCs can also influence hematopoietic stem cell (HSC) activities, here we investigated adult hematopoiesis in mice with Cre-mediated inactivation of the fibrillin-1 (Fbn1) gene in the mesenchyme of the forming limbs (Fbn1(Prx1-/-) mice). Analyses of 3-month-old Fbn1(Prx1-/-) mice revealed a statistically significant increase of circulating red blood cells, which a differentiation assay correlated with augmented erythropoiesis. This finding, together with evidence of fibrillin-1 deposition in erythroblastic niches, supported the notion that this extracellular matrix protein normally restricts differentiation of erythroid progenitors. Whereas flow cytometry measurements identified a decreased HSC frequency in mutant relative to wild type mice, no appreciable differences were noted with regard to the relative abundance and differentiation potential of myeloid progenitor cells. Together these findings implied that fibrillin-1 normally promotes HSC expansion but does not influence cell lineage commitment. Since local TGFβ hyperactivity has been associated with abnormal osteogenesis in Fbn1(Prx1-/-) mice, 1-month-old mutant and wild type animals were systemically treated for 8weeks with either a pan-TGF-β-neutralizing antibody or an antibody of the same IgG1 isotype. The distinct outcomes of these pharmacological interventions strongly suggest that fibrillin-1 differentially modulates TGFβ activity in HSC vs. erythroid niches.

Towards 3D in vitro models for the study of cardiovascular tissues and disease

The field of tissue engineering is developing biomimetic biomaterial scaffolds that are showing increasing therapeutic potential for the repair of cardiovascular tissues. However, a major opportunity exists to use them as 3D in vitro models for the study of cardiovascular tissues and disease in addition to drug development and testing. These in vitro models can span the gap between 2D culture and in vivo testing, thus reducing the cost, time, and ethical burden of current approaches. Here, we outline the progress to date and the requirements for the development of ideal in vitro 3D models for blood vessels, heart valves, and myocardial tissue.