Causative role of a novel intronic indel variant in FBN1 and maternal germinal mosaicism in Marfan syndrome.

BACKGROUND: Marfan syndrome (MFS) is an autosomal dominant connective tissue disease with wide clinical heterogeneity, and mainly caused by pathogenic variants in fibrillin-1 (FBN1). METHODS: A Chinese 4-generation MFS pedigree with 16 family members was recruited and exome sequencing (ES) was performed in the proband. Transcript analysis (patient RNA and minigene assays) and in silico structural analysis were used to determine the pathogenicity of the variant. In addition, germline mosaicism in family member (Ι:1) was assessed using quantitative fluorescent polymerase chain reaction (QF-PCR) and short tandem repeat PCR (STR) analyses. RESULTS: Two cis-compound benign intronic variants of FBN1 (c.3464-4 A > G and c.3464-5G > A) were identified in the proband by ES. As a compound variant, c.3464-5_3464-4delGAinsAG was found to be pathogenic and co-segregated with MFS. RNA studies indicated that aberrant transcripts were found only in patients and mutant-type clones. The variant c.3464-5_3464-4delGAinsAG caused erroneous integration of a 3 bp sequence into intron 28 and resulted in the insertion of one amino acid in the protein sequence (p.Ile1154_Asp1155insAla). Structural analyses suggested that p.Ile1154_Asp1155insAla affected the protein's secondary structure by interfering with one disulfide bond between Cys1140 and Cys1153 and causing the extension of an anti-parallel ß sheet in the calcium-binding epidermal growth factor-like (cbEGF)13 domain. In addition, the asymptomatic family member Ι:1 was deduced to be a gonadal mosaic as assessed by inconsistent results of sequencing and STR analysis. CONCLUSIONS: To our knowledge, FBN1 c.3464-5_3464-4delGAinsAG is the first identified pathogenic intronic indel variant affecting non-canonical splice sites in this gene. Our study reinforces the importance of assessing the pathogenic role of intronic variants at the mRNA level, with structural analysis, and the occurrence of mosaicism.

Multidisciplinary follow-up in a patient with Morgagni hernia leads to diagnosis of Marfan syndrome.

BACKGROUND: congenital diaphragmatic hernia (CDH) is a birth defect occurring in isolated or syndromic (chromosomal or monogenic) conditions. The diaphragmatic defect can be the most common one: left-sided posterolateral, named Bochdalek hernia; or it can be an anterior-retrosternal defect, named Morgagni hernia. Marfan syndrome (MFS) is a rare autosomal dominant inherited condition that affects connective tissue, caused by mutations in fibrillin-1 gene on chromosome 15. To date various types of diaphragmatic defects (about 30 types) have been reported in association with MFS, but they are heterogeneous, including CDH and paraesophageal hernia. CASE PRESENTATION: We describe the case of a child incidentally diagnosed with Morgagni hernia through a chest X-ray performed due to recurrent respiratory tract infections. Since the diagnosis of CDH, the patient underwent a clinical multidisciplinary follow-up leading to the diagnosis of MFS in accordance with revised Ghent Criteria: the child had typical clinical features and a novel heterozygous de novo single-base deletion in exon 26 of the FBN1 gene, identified by Whole-Exome Sequencing. MFS diagnosis permitted to look for cardiovascular complications and treat them, though asymptomatic, in order to prevent major cardiovascular life-threatening events. CONCLUSION: Our case shows the importance of a long-term and multidisciplinary follow-up in all children with diagnosis of CDH.

High-Throughput Genomics Identify Novel FBN1/2 Variants in Severe Neonatal Marfan Syndrome and Congenital Heart Defects.

Fibrillin-1 and fibrillin-2, encoded by FBN1 and FBN2, respectively, play significant roles in elastic fiber assembly, with pathogenic variants causing a diverse group of connective tissue disorders such as Marfan syndrome (MFS) and congenital contractural arachnodactyly (CCD). Different genomic variations may lead to heterogeneous phenotypic features and functional consequences. Recent high-throughput sequencing modalities have allowed detection of novel variants that may guide the care for patients and inform the genetic counseling for their families. We performed clinical phenotyping for two newborn infants with complex congenital heart defects. For genetic investigations, we employed next-generation sequencing strategies including whole-genome Single-Nucleotide Polymorphism (SNP) microarray for infant A with valvular insufficiency, aortic sinus dilatation, hydronephrosis, and dysmorphic features, and Trio whole-exome sequencing (WES) for infant B with dextro-transposition of the great arteries (D-TGA) and both parents. Infant A is a term male with neonatal marfanoid features, left-sided hydronephrosis, and complex congenital heart defects including tricuspid regurgitation, aortic sinus dilatation, patent foramen ovale, patent ductus arteriosus, mitral regurgitation, tricuspid regurgitation, aortic regurgitation, and pulmonary sinus dilatation. He developed severe persistent pulmonary hypertension and worsening acute hypercapnic hypoxemic respiratory failure, and subsequently expired on day of life (DOL) 10 after compassionate extubation. Cytogenomic whole-genome SNP microarray analysis revealed a deletion within the FBN1 gene spanning exons 7-30, which overlapped with the exon deletion hotspot region associated with neonatal Marfan syndrome. Infant B is a term male prenatally diagnosed with isolated D-TGA. He required balloon atrial septostomy on DOL 0 and subsequent atrial switch operation, atrial septal defect repair, and patent ductus arteriosus ligation on DOL 5. Trio-WES revealed compound heterozygous c.518C>T and c.8230T>G variants in the FBN2 gene. Zygosity analysis confirmed each of the variants was inherited from one of the parents who were healthy heterozygous carriers. Since his cardiac repair at birth, he has been growing and developing well without any further hospitalization. Our study highlights novel FBN1/FBN2 variants and signifies the phenotype-genotype association in two infants affected with complex congenital heart defects with and without dysmorphic features. These findings speak to the importance of next-generation high-throughput genomics for novel variant detection and the phenotypic variability associated with FBN1/FBN2 variants, particularly in the neonatal period, which may significantly impact clinical care and family counseling.

Microfibril-associated glycoprotein 4 forms octamers that mediate interactions with elastogenic proteins and cells.

Microfibril-associated glycoprotein 4 (MFAP4) is a 36-kDa extracellular matrix glycoprotein with critical roles in organ fibrosis, chronic obstructive pulmonary disease, and cardiovascular disorders, including aortic aneurysms. MFAP4 multimerises and interacts with elastogenic proteins, including fibrillin-1 and tropoelastin, and with cells via integrins. Structural details of MFAP4 and its potential interfaces for these interactions are unknown. Here, we present a cryo-electron microscopy structure of human MFAP4. In the presence of calcium, MFAP4 assembles as an octamer, where two sets of homodimers constitute the top and bottom halves of each octamer. Each homodimer is linked together by an intermolecular disulphide bond. A C34S missense mutation prevents disulphide-bond formation between monomers but does not prevent octamer assembly. The atomic model, built into the 3.55 Å cryo-EM map, suggests that salt-bridge interactions mediate homodimer assembly, while non-polar residues form the interface between octamer halves. In the absence of calcium, an MFAP4 octamer dissociates into two tetramers. Binding studies with fibrillin-1, tropoelastin, LTBP4, and small fibulins show that MFAP4 has multiple surfaces for protein-protein interactions, most of which depend upon MFAP4 octamer assembly. The C34S mutation does not affect these protein interactions or cell interactions. MFAP4 assemblies with fibrillin-1 abrogate MFAP4 interactions with cells.

Wnt Signaling Inhibition Prevents Postnatal Inflammation and Disease Progression in Mouse Congenital Myxomatous Valve Disease.

BACKGROUND: Myxomatous valve disease (MVD) is the most common cause of mitral regurgitation, leading to impaired cardiac function and heart failure. MVD in a mouse model of Marfan syndrome includes valve leaflet thickening and progressive valve degeneration. However, the underlying mechanisms by which the disease progresses remain undefined. METHODS: Mice with Fibrillin 1 gene variant Fbn1C1039G/+ recapitulate histopathologic features of Marfan syndrome, and Wnt (Wingless-related integration site) signaling activity was detected in TCF/Lef-lacZ (T-cell factor/lymphoid enhancer factor-ß-galactosidase) reporter mice. Single-cell RNA sequencing was performed from mitral valves of wild-type and Fbn1C1039G/+ mice at 1 month of age. Inhibition of Wnt signaling was achieved by conditional induction of the secreted Wnt inhibitor Dkk1 (Dickkopf-1) expression in periostin-expressing valve interstitial cells of Periostin-Cre; tetO-Dkk1; R26rtTA; TCF/Lef-lacZ; Fbn1C1039G/+ mice. Dietary doxycycline was administered for 1 month beginning with MVD initiation (1-month-old) or MVD progression (2-month-old). Histological evaluation and immunofluorescence for ECM (extracellular matrix) and immune cells were performed. RESULTS: Wnt signaling is activated early in mitral valve disease progression, before immune cell infiltration in Fbn1C1039G/+ mice. Single-cell transcriptomics revealed similar mitral valve cell heterogeneity between wild-type and Fbn1C1039G/+ mice at 1 month of age. Wnt pathway genes were predominantly expressed in valve interstitial cells and valve endothelial cells of Fbn1C1039G/+ mice. Inhibition of Wnt signaling in Fbn1C1039G/+ mice at 1 month of age prevented the initiation of MVD as indicated by improved ECM remodeling and reduced valve leaflet thickness with decreased infiltrating macrophages. However, later, Wnt inhibition starting at 2 months did not prevent the progression of MVD. CONCLUSIONS: Wnt signaling is involved in the initiation of mitral valve abnormalities and inflammation but is not responsible for later-stage valve disease progression once it has been initiated. Thus, Wnt signaling contributes to MVD progression in a time-dependent manner and provides a promising therapeutic target for the early treatment of congenital MVD in Marfan syndrome.

Asprosin aggravates atherosclerosis via regulating the phenotype transformation of vascular smooth muscle cells.

Phenotype transformation of vascular smooth muscle cells (VSMCs) plays an important role in the development of atherosclerosis. Asprosin is a newly discovered adipokine, which is critical in regulating metabolism. However, the relationship between asprosin and phenotype transformation of VSMCs in atherosclerosis remains unclear. The aim of this study is to investigate whether asprosin affects the progression of atherosclerosis by inducing phenotype transformation of VSMCs. We established an atherosclerosis model in ApoE-/- mice and administered asprosin recombinant protein and asprosin antibody to mice. Knocking down asprosin was also as an intervention. Interestingly, we found a correlation between asprosin levels and atherosclerosis. Asprosin promoted plaque formation and phenotype transformation of VSMCs. While, AspKD or asprosin antibody reduced the plaque lesion and suppressed vascular stiffness in ApoE-/- mice. Mechanistically, asprosin induced phenotype transformation of MOVAs by binding to GPR54, leading to Gαq/11 recruitment and activation of the PLC-PKC-ERK1/2-STAT3 signaling pathway. Si GPR54 or GPR54 antagonist partially inhibited the action of asprosin in MOVAs. Mutant GPR54-(267, 307) residue cancelled the binding of asprosin and GPR54. In summary, this study confirmed asprosin activated GPR54/Gαq/11-dependent ERK1/2-STAT3 signaling pathway, thereby promoting VSMCs phenotype transformation and aggravating atherosclerosis, thus providing a new target for the treatment of atherosclerosis.

Targeted genetic analysis in a cohort of sporadic death from spontaneous rupture of thoracic aortic dissection in Han Chinese population.

PURPOSE: Thoracic aortic dissection (TAD) is a life-threatening cardiovascular disease that often results in sudden cardiac death (SCD). However, the genetic characteristics of individuals with TAD confirmed at autopsy have been rarely studied. Our objective was to determine the prevalence of pathogenic variants in TAD-associated genes in a cohort of sporadic deaths resulting from spontaneous rupture of TAD and identify relevant genotype-phenotype relationships in Han Chinese population. METHODS: We included sixty-one consecutive sporadic decedents whose primary cause of death was spontaneous rupture of TAD, and performed a whole exome sequencing based strategy comprising 26 known TAD-associated genes. RESULTS: We identified 7 pathogenic or likely pathogenic (P/LP) variants in 7 cases (11.48 %) and 22 variants of uncertain significance (VUS) in 22 cases (36.07 %). The FBN1 gene was found to be the major disease-causing gene. Notably, TAD decedents with P/LP variant exhibited significantly earlier mortality. Moreover, we reported for the first time that TAD decedents with P/LP variant had a shorter diagnosis and treatment time. CONCLUSION: Our study investigated the genetic characteristics of TAD individuals confirmed until autopsy in Han Chinese population. The findings enhanced the understanding of the genetic underpinnings of TAD and have significant implications for clinical management and forensic investigations.

In vivo phenotypic vascular dysfunction extends beyond the aorta in a mouse model for fibrillin-1 (Fbn1) mutation.

In individuals with Marfan Syndrome (MFS), fibrillin-1 gene (FBN1) mutations can lead to vascular wall weakening and dysfunction. The experimental mouse model of MFS (Fbn1C1041G/+) has been advantageous in investigating MFS-associated life-threatening aortic aneurysms. It is well established that the MFS mouse model exhibits an accelerated-aging phenotype in elastic organs like the aorta, lung, and skin. However, the impact of Fbn1 mutations on the in vivo function and structure of various artery types with the consideration of sex and age, has not been adequately explored in real-time and a clinically relevant context. In this study, we investigate if Fbn1 mutation contributes to sex-dependent alterations in central and cerebral vascular function similar to phenotypic changes associated with normal aging in healthy control mice. In vivo ultrasound imaging of central and cerebral vasculature was performed in 6-month-old male and female MFS and C57BL/6 mice and sex-matched 12-month-old (middle-aged) healthy control mice. Our findings confirm aortic enlargement (aneurysm) and wall stiffness in MFS mice, but with exacerbation in male diameters. Coronary artery blood flow velocity (BFV) in diastole was not different but left pulmonary artery BFV was decreased in MFS and 12-month-old control mice regardless of sex. At 6 months of age, MFS male mice show decreased posterior cerebral artery BFV as compared to age-matched control males, with no difference observed between female cohorts. Reduced mitral valve early-filling velocities were indicated in MFS mice regardless of sex. Male MFS mice also demonstrated left ventricular hypertrophy. Overall, these results underscore the significance of biological sex in vascular function and structure in MFS mice, while highlighting a trend of pre-mature vascular aging phenotype in MFS mice that is comparable to phenotypes observed in older healthy controls. Furthermore, this research is a vital step in understanding MFS's broader implications and sets the stage for more in-depth future analyses, while providing data-driven preclinical justification for re-evaluating diagnostic approaches and therapeutic efficacy.

Pathogenic variants affecting the TB5 domain of the fibrillin-1 protein: not only in geleophysic/acromicric dysplasias but also in Marfan syndrome.

BACKGROUND: Marfan syndrome (MFS) is a multisystem disease with a unique combination of skeletal, cardiovascular and ocular features. Geleophysic/acromicric dysplasias (GPHYSD/ACMICD), characterised by short stature and extremities, are described as 'the mirror image' of MFS. The numerous FBN1 pathogenic variants identified in MFS are located all along the gene and lead to the same final pathogenic sequence. Conversely, in GPHYSD/ACMICD, the 28 known heterozygous FBN1 pathogenic variants all affect exons 41-42 encoding TGFß-binding protein-like domain 5 (TB5). METHODS: Since 1996, more than 5000 consecutive probands have been referred nationwide to our laboratory for molecular diagnosis of suspected MFS. RESULTS: We identified five MFS probands carrying distinct heterozygous pathogenic in-frame variants affecting the TB5 domain of FBN1. The clinical data showed that the probands displayed a classical form of MFS. Strikingly, one missense variant affects an amino acid that was previously involved in GPHYSD. CONCLUSION: Surprisingly, pathogenic variants in the TB5 domain of FBN1 can lead to two opposite phenotypes: GPHYSD/ACMICD and MFS, suggesting the existence of different pathogenic sequences with the involvement of tissue specificity. Further functional studies are ongoing to determine the precise role of this domain in the physiopathology of each disease.

Enhanced Optic Nerve Expansion and Altered Ultrastructure of Elastic Fibers Induced by Lysyl Oxidase Inhibition in a Mouse Model of Marfan Syndrome.

Two major constituents of exfoliation material, fibrillin-1 and lysyl oxidase-like 1 (encoded by FBN1 and LOXL1), are implicated in exfoliation glaucoma, yet their individual contributions to ocular phenotype are minor. To test the hypothesis that a combination of FBN1 mutation and LOXL1 deficiency exacerbates ocular phenotypes, the pan-lysyl oxidase inhibitor ß-aminopropionitrile (BAPN) was used to treat adult wild-type (WT) mice and mice heterozygous for a missense mutation in Fbn1 (Fbn1C1041G/+) for 8 weeks and their eyes were examined. Although intraocular pressure did not change and exfoliation material was not detected in the eyes, BAPN treatment worsened optic nerve and axon expansion in Fbn1C1041G/+ mice, an early sign of axonal damage in rodent models of glaucoma. Disruption of elastic fibers was detected only in Fbn1C1041G/+ mice, which increased with BAPN treatment, as shown by histologic and immunohistochemical staining of the optic nerve pia mater. Transmission electron microscopy showed that Fbn1C1041G/+ mice had fewer microfibrils, smaller elastin cores, and a lower density of elastic fibers compared with WT mice in control groups. BAPN treatment led to elastin core expansion in both WT and Fbn1C1041G/+ mice, but an increase in the density of elastic fiber was confined to Fbn1C1041G/+ mice. LOX inhibition had a stronger effect on optic nerve and elastic fiber parameters in the context of Fbn1 mutation, indicating the Marfan mouse model with LOX inhibition warrants further investigation for exfoliation glaucoma pathogenesis.

[Clinical phenotype and genetic analysis of six Chinese patients affected with Acromicric dysplasia due to variants of FBN1 gene].

OBJECTIVE: To retrospectively analyze the clinical and genetic characteristics of six patients with Acromicric dysplasia due to variants of the FBN1 gene. METHODS: Six patients who had visited the Affiliated Hospital of Qingdao University between February 2018 and October 2020 were selected as the study subjects. Clinical data of the patients were collected. High-throughput sequencing was carried out. And candidate variants were verified by Sanger sequencing. RESULTS: All of the six patients had presented with severe short stature (< 3s), brachydactyly, short and broad hands and feet. Other manifestations included joint stiffness, facial dysmorphism, delayed bone age, liver enlargement, coracoid femoral head, and lumbar lordosis. Genetic testing revealed that all had harbored heterozygous variants of the FBN1 gene. Patient 1 had harbored a c.5183C>T (p.A1728V) missense variant in exon 42, which had derived from his father (patient 2). Patient 3 had harbored a c.5284G>A (p.G1762S) missense variant in exon 43, which had derived from her mother (patient 4). Patient 5 had harbored a c.5156G>T (p.C1719F) missense variant in exon 42, which was de novo in origin. Patient 6 had harbored a c.5272G>T (p.D1758Y) missense variant in exon 43, which was also de novo in origin. The variants carried by patients 1, 3 and 6 were known to be pathogenic. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the FBN1: c.5156G>T was rated as a pathogenic variant (PS2+PM1+PM2_Supporting +PM5+PP3). CONCLUSION: All of the six patients had severe short stature and a variety of other clinical manifestations, which may be attributed to the variants of the FBN1 gene.

The role of genetic testing in Marfan syndrome.

PURPOSE OF REVIEW: This review aims to delineate the genetic basis of Marfan syndrome (MFS) and underscore the pivotal role of genetic testing in the diagnosis, differential diagnosis, genotype-phenotype correlations, and overall disease management. RECENT FINDINGS: The identification of pathogenic or likely pathogenic variants in the FBN1 gene, associated with specific clinical features such as aortic root dilatation or ectopia lentis, is a major diagnostic criterion for MFS. Understanding genotype-phenotype correlations is useful for determining the timing of follow-up, guiding prophylactic aortic root surgery, and providing more precise information to patients and their family members during genetic counseling. Genetic testing is also relevant in distinguishing MFS from other conditions that present with heritable thoracic aortic diseases, allowing for tailored and individualized management. SUMMARY: Genetic testing is essential in different steps of the MFS patients' clinical pathway, starting from the phase of diagnosis to management and specific treatment.

Aqueous humor TGFß and fibrillin-1 in Tsk mice reveal clues to POAG pathogenesis.

Aqueous humor (AH) and blood levels of transforming growth factor ß (TGFß) are elevated in idiopathic primary open angle glaucoma (POAG) representing a disease biomarker of unclear status and function. Tsk mice display a POAG phenotype and harbor a mutation of fibrillin-1, an important regulator of TGFß bioavailability. AH TGFß2 was higher in Tsk than wild-type (WT) mice (by 34%; p = 0.002; ELISA); similarly, AH TGFß2 was higher in human POAG than controls (2.7-fold; p = 0.00005). As in POAG, TGFß1 was elevated in Tsk serum (p = 0.01). Fibrillin-1 was detected in AH from POAG subjects and Tsk mice where both had similar levels relative to controls (p = 0.45). 350 kDa immunoblot bands representing WT full-length fibrillin-1 were present in human and mouse AH. A 418 kDa band representing mutant full-length fibrillin-1 was present only in Tsk mice. Lower molecular weight fibrillin-1 antibody-reactive bands were present in similar patterns in humans and mice. Certain bands (130 and 32 kDa) were elevated only in human POAG and Tsk mice (p ≤ 0.04 relative to controls) indicating discrete isoforms relevant to disease. In addition to sharing a phenotype, Tsk mice and human POAG subjects had common TGFß and fibrillin-1 features in AH and also blood that are pertinent to understanding glaucoma pathogenesis.

Identification of two novel large deletions in FBN1 gene by next-generation sequencing and multiplex ligation-dependent probe amplification.

BACKGROUND: Mutations in fibrillin-1 (FBN1) are known to be associated with Marfan syndrome (MFS), an autosomal dominant connective tissue disorder. Most FBN1 mutations are missense or nonsense mutations. Traditional molecular genetic testing for the FBN1 gene, like Sanger sequencing, may miss disease-causing mutations in the gene's regulatory regions or non-coding sequences, as well as partial or complete gene deletions and duplications. METHODS: Next-generation sequencing, multiplex ligation-dependent probe amplification and gap PCR were conducted on two MFS patients to screen for disease-causing mutations. RESULTS: We identified two large deletions in FBN1 from two MFS patients. One patient had a 0.23 Mb deletion (NC_000015.9:g.48550506_48779360del) including 5'UTR-exon6 of FBN1. The other patient harbored a 1416 bp deletion (NC_000015.9:g.48410869_48412284del) affecting the last exon, exon 66, of the FBN1 gene. CONCLUSION: Our results expanded the number of large FBN1 deletions and highlighted the importance of screening for large deletions in FBN1 in clinical genetic testing, especially for those with the classic MFS phenotype.

Curcumin Promotes Diabetic Foot Ulcer Wound Healing by Inhibiting miR-152-3p and Activating the FBN1/TGF-ß Pathway.

The objective of this study was to investigate the mechanism of curcumin in diabetic foot ulcer (DFU) wound healing. A DFU rat model was established, and fibroblasts were cultured in a high-glucose (HG) environment to create a cell model. Various techniques, including Western blot, RT‒qPCR, flow cytometry, Transwell, cell scratch test and H&E staining, were employed to measure the levels of relevant genes and proteins, as well as to assess cell proliferation, apoptosis, migration, and pathological changes. The results showed that miR-152-3p was overexpressed in DFU patients, while FBN1 was underexpressed. Curcumin was found to inhibit fibroblast apoptosis, promote proliferation, migration, and angiogenesis in DFU rats, and accelerate wound healing in DFU rats. In addition, overexpression of miR-152-3p weakened the therapeutic effect of curcumin, while overexpression of FBN1 reversed the effects of the miR-152-3p mimic. Further investigations into the underlying mechanisms revealed that curcumin expedited wound healing in DFU rats by restoring the FBN1/TGF-ß pathway through the inhibition of miR-152-3p. In conclusion, curcumin can suppress the activity of miR-152-3p, which, in turn, leads to the rejuvenation of the FBN1/TGF-ß pathway and accelerates DFU wound healing.

Dynamic changes in mitral valve extracellular matrix, tissue mechanics and function in a mouse model of Marfan syndrome.

OBJECTIVE: Mouse models of Marfan syndrome (MFS) with Fibrillin 1 (Fbn1) variant C1041G exhibit cardiovascular abnormalities, including myxomatous valve disease (MVD) and aortic aneurism, with structural extracellular matrix (ECM) dysregulation. In this study, we examine the structure-function-mechanics relations of the mitral valve related to specific transitions in ECM composition and organization in progressive MVD in MFS mice from Postnatal day (P)7 to 1 year-of-age. APPROACH AND RESULTS: Mechanistic links between mechanical forces and biological changes in MVD progression were examined in Fbn1C1041G/+ MFS mice. By echocardiography, mitral valve dysfunction is prevalent at 2 months with a decrease in cardiac function at 6 months, followed by a preserved cardiac function at 12 months. Mitral valve (MV) regurgitation occurs in a subset of mice at 2-6 months, while progressive dilatation of the aorta occurs from 2 to 12 months. Mitral valve tissue mechanical assessments using a uniaxial Permeabilizable Fiber System demonstrate decreased stiffness of MFS MVs at all stages. Histological and microscopic analysis of ECM content, structure, and fiber orientation demonstrate that alterations in ECM mechanics, composition, and organization precede functional abnormalities in Fbn1C1041G/+MFS MVs. At 2 months, ECM abnormalities are detected with an increase in proteoglycans and decreased stiffness of the mitral valve. By 6-12 months, collagen fiber remodeling is increased with abnormal fiber organization in MFS mitral valve leaflets. At the same time, matrifibrocyte gene expression characteristic of collagen-rich connective tissue is increased, as detected by RNA in situ hybridization and qPCR. Together, these studies demonstrate early prevalence of proteoglycans at 2 months followed by upregulation of collagen structure and organization with age in MVs of MFS mice. CONCLUSIONS: Altogether, our data indicate dynamic regulation of mitral valve structure, tissue mechanics, and function that reflect changes in ECM composition, organization, and gene expression in progressive MVD. Notably, increased collagen fiber organization and orientation, potentially dependent on increased matrifibrocyte cell activity, is apparent with altered mitral valve mechanics and function in aging MFS mice.

Three-dimensional co-culturing of stem cell-derived cardiomyocytes and cardiac fibroblasts reveals a role for both cell types in Marfan-related cardiomyopathy.

Pathogenic variants in the FBN1 gene, which encodes the extracellular matrix protein fibrillin-1, cause Marfan syndrome (MFS), which affects multiple organ systems, including the cardiovascular system. Myocardial dysfunction has been observed in a subset of patients with MFS and in several MFS mouse models. However, there is limited understanding of the intrinsic consequences of FBN1 variants on cardiomyocytes (CMs). To elucidate the CM-specific contribution in Marfan's cardiomyopathy, cardiosphere cultures of CMs and cardiac fibroblasts (CFs) are used. CMs and CFs were derived by human induced pluripotent stem cell (iPSC) differentiation from MFS iPSCs with a pathogenic variant in FBN1 (c.3725G>A; p.Cys1242Tyr) and the corresponding CRISPR-corrected iPSC line (Cor). Cardiospheres containing MFS CMs show decreased FBN1, COL1A2 and GJA1 expression. MFS CMs cultured in cardiospheres have fewer binucleated CMs in comparison with Cor CMs. 13% of MFS CMs in cardiospheres are binucleated and 15% and 16% in cardiospheres that contain co-cultures with respectively MFS CFs and Cor CFs, compared to Cor CMs, that revealed up to 23% binucleation when co-cultured with CFs. The sarcomere length of CMs, as a marker of development, is significantly increased in MFS CMs interacting with Cor CF or MFS CF, as compared to monocultured MFS CMs. Nuclear blebbing was significantly more frequent in MFS CFs, which correlated with increased stiffness of the nuclear area compared to Cor CFs. Our cardiosphere model for Marfan-related cardiomyopathy identified a contribution of CFs in Marfan-related cardiomyopathy and suggests that abnormal early development of CMs may play a role in the disease mechanism.

Overcoming challenges associated with identifying FBN1 deep intronic variants through whole-genome sequencing.

BACKGROUND: Marfan syndrome (MFS), caused by pathogenic variants of FBN1 (fibrillin-1), is a systemic connective tissue disorder with variable phenotypes and treatment responsiveness depending on the variant. However, a significant number of individuals with MFS remain genetically unexplained. In this study, we report novel pathogenic intronic variants in FBN1 in two unrelated families with MFS. METHODS: We evaluated subjects with suspected MFS from two unrelated families using Sanger sequencing or multiplex ligation-dependent probe amplification of FBN1 and/or panel-based next-generation sequencing. As no pathogenic variants were identified, whole-genome sequencing was performed. Identified variants were analyzed by reverse transcription-PCR and targeted sequencing of FBN1 mRNA harvested from peripheral blood or skin fibroblasts obtained from affected probands. RESULTS: We found causative deep intronic variants, c.6163+1484A>T and c.5788+36C>A, in FBN1. The splicing analysis revealed an insertion of in-frame or out-of-frame intronic sequences of the FBN1 transcript predicted to alter function of calcium-binding epidermal growth factor protein domain. Family members carrying c.6163+1484A>T had high systemic scores including prominent skeletal features and aortic dissection with lesser aortic dilatation. Family members carrying c.5788+36C>A had more severe aortic root dilatation without aortic dissection. Both families had ectopia lentis. CONCLUSION: Variable penetrance of the phenotype and negative genetic testing in MFS families should raise the possibility of deep intronic FBN1 variants and the need for additional molecular studies. This study expands the mutation spectrum of FBN1 and points out the importance of intronic sequence analysis and the need for integrative functional studies in MFS diagnosis.

The usefulness of the genetic panel in the classification and refinement of diagnostic accuracy of Mexican patients with Marfan syndrome and other connective tissue disorders.

Marfan syndrome (MFS) is a multisystem genetic disorder with over 3000 mutations described in the fibrillin 1 (FBN1) gene. Like MFS, other connective tissue disorders also require a deeper understanding of the phenotype-genotype relationship due to the complexity of the clinical presentation, where diagnostic criteria often overlap. Our objective was to identify mutations in patients with connective tissue disorders using a genetic multipanel and to analyze the genotype-phenotype associations in a cohort of Mexican patients. We recruited 136 patients with MFS and related syndromes from the National Institute of Cardiology. Mutations were identified using next-generation sequencing (NGS). To examine the correlation between mutation severity and severe cardiovascular conditions, we focused on patients who had undergone Bentall-de Bono surgery or aortic valve repair. The genetic data obtained allowed us to reclassify the initial clinical diagnosis across various types of connective tissue disorders. The transforming growth factor beta receptor 2 (TGFBR2) rs79375991 mutation was found in 10 out of 16 (63%) Loeys-Dietz patients. We observed a high prevalence (65%) of more severe mutations, such as frameshift indels and stop codons, among patients requiring invasive treatments like aortic valve-sparing surgery, Bentall and de Bono procedures, or aortic valve replacement due to severe cardiovascular injury. Although our study did not achieve precise phenotype-genotype correlations, it underscores the importance of a multigenetic panel evaluation. This could pave the way for a more comprehensive diagnostic approach and inform medical and surgical treatment decision-making.