Splicing mutation in the fibrillin-1 gene associated with neonatal Marfan syndrome and severe pulmonary emphysema with tracheobronchomalacia

Neonatal Marfan syndrome: a case report of a novel fibrillin 1 mutation, with genotype-phenotype correlation and brief review of the literature

BACKGROUND

Neonatal Marfan syndrome (nMFS) is a rare condition characterized by severe phenotype and poor prognosis. nMFS is caused by mutations in a specific region of the fibrillin 1 gene (FBN1). Prompt recognition of typical signs of neonatal presentation, such as characteristic facial anomalies with senile appearance, arthrogryposis, and campto-arachnodactyly, is fundamental for performing an early cardiological examination. This usually reveals rapidly progressive cardiovascular disease due to severe atrioventricular valve dysfunction.

CASE PRESENTATION

Herein, we report the case of an early-onset cardiac failure in a neonate with Marfan syndrome, with a brief review of the literature of cases with cardiac involvement in neonatal age. Clinical exome sequencing identified the novel heterozygous de novo missense variant c.3152T > G in FBN1 gene (NM_000138.4), causing the aminoacidic change p.Phe1051Cys. Phenotype-genotype correlation led to a multidisciplinary diagnostic and management workflow.

CONCLUSION

The prompt recognition of a typical phenotype such as that of Marfan syndrome should lead to a detailed evaluation and close follow-up of cardiac morphology and function. Indeed, multi-disciplinary evaluation based on genotype-phenotype correlations of nMFS cases is essential to finding out the best medical and surgical approach, predicting the relevant impact on patient prognosis, and adequately counseling their families.

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.

Unique Features of Cardiovascular Involvement and Progression in Children with Marfan Syndrome Justify Dedicated Multidisciplinary Care

Marfan syndrome (MIM: # 154700; MFS) is an autosomal dominant disease representing the most common form of heritable connective tissue disorder. The condition presents variable multiorgan expression, typically involving a triad of cardiovascular, eye, and skeletal manifestations. Other multisystemic features are often underdiagnosed. Moreover, the disease is characterized by age related penetrance. Diagnosis and management of MFS in the adult population are well-described in literature. Few studies are focused on MFS in the pediatric population, making the clinical approach (cardiac and multiorgan) to these cases challenging both in terms of diagnosis and serial follow-up. In this review, we provide an overview of MFS manifestations in children, with extensive revision of major organ involvement (cardiovascular ocular and skeletal). We attempt to shed light on minor aspects of MFS that can have a significant progressive impact on the health of affected children. MFS is an example of a syndrome where an early personalized approach to address a dynamic, genetically determined condition can make a difference in outcome. Applying an early multidisciplinary clinical approach to MFS cases can prevent acute and chronic complications, offer tailored management, and improve the quality of life of patients.

Genotype-phenotype spectrum and prognosis of early-onset Marfan syndrome

BACKGROUND

Marfan syndrome is a genetic connective tissue disorder affecting skeletal, ocular, and cardiovascular organ systems. Previous research found that pathogenic variants clustered in exons 24-32 of fibrillin-1 (FBN1) gene result in more severe clinical phenotypes. Furthermore, genotype-phenotype correlation studies suggested that more severe cardiovascular phenotypes were related to variants held responsible for haploinsufficiency. Our objective was to analyze the differences in clinical manifestations and genotypes of individuals with early-onset Marfan syndrome and to assess their impact on management strategies.

METHODS

We analyzed clinical and genetic data of a new patient with early-onset Marfan syndrome together with 51 previously reported ones in the PubMed database between 1991 and 2022.

RESULTS

Analysis showed 94% (49/52) of pathogenic variants clustered in exons 24-32 of the FBN1. The most common skeletal features were arachnodactyly (98%), reduced elbow extension (48%), pectus deformity (40%), and scoliosis (39%). Haploinsufficiency variants were reported as having poor outcome in 87.5% of the cases. Among patients carrying variants that substitute a cysteine for another amino acid and those that do not change cysteine content, cardiac intervention was found to be associated with a better outcome (p = 0.035 vs. p = 0.002). Variants that create an extra cysteine residue were found to be associated with a higher risk of ectopia lentis. Additionally, children up to 36-months-old were more often reported as still alive at the time of publication compared to newborns (p < 0.01).

CONCLUSIONS

Our findings have implications for prognosis, because different genotype groups and their resulting phenotype may require personalized care and management.

Enhanced Notch3 signaling contributes to pulmonary emphysema in a Murine Model of Marfan syndrome

Marfan syndrome (MFS) is a heritable disorder of connective tissue, caused by mutations in the fibrillin-1 gene. Pulmonary functional abnormalities, such as emphysema and restrictive lung diseases, are frequently observed in patients with MFS. However, the pathogenesis and molecular mechanism of pulmonary involvement in MFS patients are underexplored. Notch signaling is essential for lung development and the airway epithelium regeneration and repair. Therefore, we investigated whether Notch3 signaling plays a role in pulmonary emphysema in MFS. By using a murine model of MFS, fibrillin-1 hypomorphic mgR mice, we found pulmonary emphysematous-appearing alveolar patterns in the lungs of mgR mice. The septation in terminal alveoli of lungs in mgR mice was reduced compared to wild type controls in the early lung development. These changes were associated with increased Notch3 activation. To confirm that the increased Notch3 signaling in mgR mice was responsible for structure alterations in the lungs, mice were treated with N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglucine t-butyl ester (DAPT), a γ-secretase inhibitor, which inhibits Notch signaling. DAPT treatment reduced lung cell apoptosis and attenuated pulmonary alteration in mice with MFS. This study indicates that Notch3 signaling contributes to pulmonary emphysema in mgR mice. Our results may have the potential to lead to novel strategies to prevent and treat pulmonary manifestations in patients with MFS.

Detection of ten novel FBN1 mutations in Chinese patients with typical or incomplete Marfan syndrome and an overview of the genotype-phenotype correlations

OBJECTIVE

The aim of this study is to identify the mutation spectrum of FBN1 in patients with Marfan syndrome (MFS) or Marfan-Like Phenotypes and to analyze the genotype-phenotype correlations of existing literature.

METHODS AND RESULTS

A total of 21 unrelated patients with a definite or suspected clinical diagnosis of MFS were recruited for research. Eleven FBN1 mutations were identified in 12 patients who strictly fulfilled the Ghent criteria for MFS, and 1 FBN1 mutations were detected in 9 patients with suspected MFS by screening the mutations of FBN1. These FBN1 mutations include 10 novel mutations (c.357 C>A, c.493 C>T, c.1374 T>A, c.4143 delG, c. 6987 C>G, c.7238 G>A, c. 7765 A>G, c.8200 A>G, c. 8431 G>A, c.8547 T>G,) and 2 previously reported mutations (c.4567 C>T, c.4615 C>T). By searching PubMed and Embase (from 1990 up to December 2018), twenty nine studies (including the present study) with 890 subjects with MFS or Marfan-like phenotypes were included to analyze the genotype-phenotype correlations. Several genotype-phenotype correlations were founded. Firstly, mutations of premature termination codons (PTC) were associated with an increased risk of major cardiovascular involvements. Secondly, the frequency of patients with major cardiovascular involvement in exons 43-65 group was as high as that in exons 24-32 group (71.4% vs. 77.0%; p = 0.238). Finally, cysteine missense mutations might be associated with major cardiovascular involvements.

CONCLUSIONS

These results extended the FBN1 mutation spectrum of this rare disease and revealed the genotype-phenotype correlations in MFS by analyzing existing literature.

Perinatal diagnosis and management of early-onset Marfan syndrome: case report and systematic review

Early onset Marfan syndrome is the most severe form of Marfan syndrome diagnosed during perinatal period. Early onset Marfan syndrome is associated with high mortality rates, usually within the first 2 years of life. First, we present a case of prenatally diagnosed early onset Marfan syndrome in a dichorionic diamniotic twin pregnancy, where suspicion was raised at 35 weeks of gestation. Ultrasound and fetal magnetic resonance imaging were used to assess prenatal findings in the affected fetus. She presented right diaphragmatic eventration, elongation of humerus and femur and subluxation of the crystalline lens. She died 3 months after birth. Secondly, we present a PubMed-based review of the published articles on early onset Marfan syndrome, with pre- or postnatal suspicion or diagnosis. We found 39 articles published between 1981 and 2017, arising information on 55 cases. Including ours, early onset Marfan syndrome was prenatally diagnosed in 34.54% of the cases. In these cases, the most frequent prenatal findings were cardiomegaly, dilatation of the great vessels and mitral or tricuspid regurgitation. Mortality rate during the first 15 months after birth was 73.68%. In the postnatally diagnosed cases, the most frequent findings were arachnodactyly, dilatation of the great vessels and mitral or tricuspid regurgitation. Mortality rate was 61.11%. Overall genetic confirmation was performed in 67.27% of the cases. Prenatal diagnosis of early onset Marfan syndrome is challenging but of utmost importance, since management should take place in a tertiary care center, by a multidisciplinary team. Differential diagnosis is essential in order to perform an adequate genetic counseling.

Infantile Marfan syndrome in a Korean tertiary referral center

Purpose

Infantile Marfan syndrome (MFS) is a rare congenital inheritable connective tissue disorder with poor prognosis. This study aimed to evaluate the cardiovascular manifestations and overall prognosis of infantile MFS diagnosed in a tertiary referral center in Korea.

Methods

Eight patients diagnosed with infantile MFS between 2004 and 2014 were retrospectively evaluated.

Results

Their median age at the time of diagnosis was 2.5 months (range, 0–20 months). The median follow-up period was 25.5 months (range, 0–94 months). The median length at birth was 50.0 cm (range, 48–53 cm); however, height became more prominent over time, and the patients were taller than the 97th percentile at the time of the study. None of the patients had any relevant family history. Four of the 5 patients who underwent DNA sequencing had a fibrillin 1 gene mutation. All the patients with echocardiographic data of the aortic root had a z score of >2. All had mitral and tricuspid valve prolapse, and various degrees of mitral and tricuspid regurgitation. Five patients underwent open-heart surgery, including mitral valve replacement, of whom two required multiple operations. The median age at mitral valve replacement was 28.5 months (range, 5–69 months). Seven patients showed congestive heart failure before surgery or during follow-up, and required multiple anti-heart failure medications. Four patients died of heart failure at a median age of 12 months.

Conclusion

The prognosis of infantile MFS is poor; thus, early diagnosis and timely cautious treatment are essential to prevent further morbidity and mortality.

Genetic susceptibility

Why only 20% of smokers develop clinically relevant chronic obstructive pulmonary disease (COPD) was a puzzle for many years. Now, epidemiologic studies point clearly toward a large heritable component. The combination of genome-wide association studies and candidate gene analysis is helping to identify those genetic variants responsible for an individual's susceptibility to developing COPD. In this review, the current data implicating specific loci and genes in the pathogenesis of COPD are examined.

Copper deficiency induced emphysema is associated with focal adhesion kinase inactivation

BACKGROUND

Copper is an important regulator of hypoxia inducible factor 1 alpha (HIF-1α) dependent vascular endothelial growth factor (VEGF) expression, and is also required for the activity of lysyl oxidase (LOX) to effect matrix protein cross-linking. Cell detachment from the extracellular matrix can induce apoptosis (anoikis) via inactivation of focal adhesion kinase (FAK).

METHODOLOGY

To examine the molecular mechanisms whereby copper depletion causes the destruction of the normal alveolar architecture via anoikis, Male Sprague-Dawley rats were fed a copper deficient diet for 6 weeks while being treated with the copper chelator, tetrathiomolybdate. Other groups of rats were treated with the inhibitor of auto-phosphorylation of FAK, 1,2,4,5-benzenetetraamine tetrahydrochloride (1,2,4,5-BT) or FAK small interfering RNA (siRNA).

PRINCIPAL FINDINGS

Copper depletion caused emphysematous changes, decreased HIF-1α activity, and downregulated VEGF expression in the rat lungs. Cleaved caspase-3, caspase-8 and Bcl-2 interacting mediator of cell death (Bim) expression was increased, and the phosphorylation of FAK was decreased in copper depleted rat lungs. Administration of 1,2,4,5-BT and FAK siRNA caused emphysematous lung destruction associated with increased expression of cleaved capase-3, caspase-8 and Bim.

CONCLUSIONS

These data indicate that copper-dependent mechanisms contribute to the pathogenesis of emphysema, which may be associated with decreased HIF-1α and FAK activity in the lung.

Fibroblast growth factor receptors control epithelial-mesenchymal interactions necessary for alveolar elastogenesis

RATIONALE

The mechanisms contributing to alveolar formation are poorly understood. A better understanding of these processes will improve efforts to ameliorate lung disease of the newborn and promote alveolar repair in the adult. Previous studies have identified impaired alveogenesis in mice bearing compound mutations of fibroblast growth factor (FGF) receptors (FGFRs) 3 and 4, indicating that these receptors cooperatively promote postnatal alveolar formation.

OBJECTIVES

To determine the molecular and cellular mechanisms of FGF-mediated alveolar formation.

METHODS

Compound FGFR3/FGFR4-deficient mice were assessed for temporal changes in lung growth, airspace morphometry, and genome-wide expression. Observed gene expression changes were validated using quantitative real-time RT-PCR, tissue biochemistry, histochemistry, and ELISA. Autocrine and paracrine regulatory mechanisms were investigated using isolated lung mesenchymal cells and type II pneumocytes.

MEASUREMENTS AND MAIN RESULTS

Quantitative analysis of airspace ontogeny confirmed a failure of secondary crest elongation in compound mutant mice. Genome-wide expression profiling identified molecular alterations in these mice involving aberrant expression of numerous extracellular matrix molecules. Biochemical and histochemical analysis confirmed changes in elastic fiber gene expression resulted in temporal increases in elastin deposition with the loss of typical spatial restriction. No abnormalities in elastic fiber gene expression were observed in isolated mesenchymal cells, indicating that abnormal elastogenesis in compound mutant mice is not cell autonomous. Increased expression of paracrine factors, including insulin-like growth factor-1, in freshly-isolated type II pneumocytes indicated that these cells contribute to the observed pathology.

CONCLUSIONS

Epithelial/mesenchymal signaling mechanisms appear to contribute to FGFR-dependent alveolar elastogenesis and proper airspace formation.

Identification of the minimal combination of clinical features in probands for efficient mutation detection in the FBN1 gene

Mutations identified in the fibrillin-1 (FBN1) gene have been associated with Marfan syndrome (MFS). Molecular analysis of the gene is classically performed in probands with MFS to offer diagnosis for at-risk relatives and in children highly suspected of MFS. However, FBN1 gene mutations are found in an ill-defined group of diseases termed 'type I fibrillinopathies', which are associated with an increased risk of aortic dilatation and dissection. Thus, there is growing awareness of the need to identify these non-MFS probands, for which FBN1 gene screening should be performed. To answer this need we compiled the molecular data obtained from the screening of the FBN1 gene in 586 probands, which had been addressed to our laboratory for molecular diagnosis. In this group, the efficacy of FBN1 gene screening was high in classical MFS probands (72.5%,), low (58%) in those referred for incomplete MFS and only slight (14.3%) for patients referred as possible MFS. Using recursive partitioning, we found that the best predictor of the identification of a mutation in the FBN1 gene was the presence of features in at least three organ systems, combining one major, and various minor criteria. We also show that our original recommendation of two systems involved with at least one with major criterion represents the minimal criteria because in probands not meeting these criteria, the yield of mutation identification drastically falls. This recommendation should help clinicians and biologists in identifying probands with a high probability of carrying a FBN1 gene mutation, and thus optimize biological resources.

Familial neonatal Marfan syndrome due to parental mosaicism of a missense mutation in the FBN1 gene

We present a family in which three siblings were born with neonatal Marfan syndrome (MFS) to unaffected parents. The clinical findings included joint contractures, large ears, loose skin, ectopia lentis, muscular hypoplasia, aortic root dilatation, mitral and tricuspid valve insufficiency, and pulmonary emphysema. All three siblings died due to cardiorespiratory insufficiency by 2-4 months of age. Screening of the FBN1 gene showed the heterozygous c.3257G > A (p.Cys1086Tyr) mutation in the proband. Mosaicism of the mutation was demonstrated in the somatic cells and in the germ line of the father. Although three examples of parental mosaicism for classical MFS were demonstrated previously, this is the first report of familial occurrence of neonatal MFS due to a heterozygous mutation in FBN1. In conclusion, the p.Cys1086Tyr mutation in FBN1 is consistently associated with neonatal MFS. Parental mosaicism should always be kept in mind when counseling families with MFS.

Zonular fibers, multimolecular composition as related to function (elasticity) and pathology

Zonular fibers (ZF) play an important role in accommodation. With the rapid increase over the last decade of the oldest part of the population in industrialized countries, age-dependent loss of accommodation became an increasingly important problem. It appeared therefore interesting to review old and recent literature on ZF, their composition, structure and pathological alterations. By comparing former and recent reports it appeared to us, that several previous reports were not sufficiently taken in consideration for the understanding of the rheological properties of ZF. Elastin and proteoglycans-glycosaminoglycans were reported previously as constituents of ZF. Their presence besides fibrillin, the major constituent, helps to explain the rheological properties of these fibers, and especially their elasticity and its age- and pathology-dependent decline. Our review points also to some of the major problems, which remain to be addressed by future experiments.