FBN1 Variants Research Articles

Genetic insights from a Brazilian cohort of aortopathies through targeted next-generation sequencing and FBN1 direct sequencing

Thoracic aortic diseases (or aortopathies) result from complex interactions between genetic and hemodynamic factors. Often clinically silent, these diseases can lead to lethal complications such as aortic dissection or rupture. This study focused on a Brazilian cohort of 79 individuals with thoracic aortic diseases and explored genetic factors through targeted next-generation sequencing (tNGS) of 15 priority genes and FBN1 direct sequencing. The majority of individuals had nonsyndromic aortopathy, with eight diagnosed with Marfan syndrome (MFS). Pathogenic or likely pathogenic variants (PV/LPV) were found in five genes, namely, FBN1, ACTA2, TGFBR2, MYLK, and SMAD3. Notably, novel variants in FBN1 were identified that contributed to Marfan-like phenotypes. The diagnostic yield for isolated aortopathies was 7.1%, which increased to 55.5% for syndromic cases. Variants of uncertain significance (VUS) were identified, emphasizing the need for further research and familial investigations to refine variant classifications. This study provides valuable insights into the genetic landscape of aortopathies in Brazil, aiding early diagnosis and personalized management.

Genetic variants in childhood-onset dilatation of thoracic aorta in a consanguineous population

IntroductionChildhood-onset thoracic aortic dilatation (TAD) is a heterogenous group of genetic conditions the inheritance of which is largely dominant. To our knowledge, the influence of consanguinity on childhood-onset TAD has not been addressed systematically. We aim to study a cohort of children with TAD in our highly consanguineous population. MethodsChildren with TAD were consecutively recruited. Based on the likelihood of a founder mutation, genetic test was categorized to either targeted gene testing or multi-gene sequencing, followed by genetic screening of first-degree relatives. Clinical data and outcome were reviewed. ResultsThirty-three children, from 20 families, had childhood-onset TAD. Genetic test was positive in 20 children, from 13 families, providing a yield of 65 % (13/20). The median age of onset of TAD was 4.5 years. Eight variants were detected in 4 genes (FBN1, EFEMP2, ACTA2, KANSL1) with a homozygous EFEMP2 variant found in 6 families (46.2 %). Surgical intervention was required in 14 (70 %) cases (13 with EFEMP2, 1 with FBN1 variants) at a median age of 3.5 years. All patients are alive (ages range:3–31 years). ConclusionsOur work illustrates the impact of consanguinity on the genetics of childhood-onset TAD elucidating severe presentation of recessively inherited form. Our data underscores the importance of genetic screening and early recognition of TAD to achieve excellent outcome.

Assessment of Myocardial Fibrosis in Marfan Syndrome Using Cardiac Magnetic Resonance Imaging.

Impaired myocardial function and arrhythmia are important manifestations of Marfan syndrome (MFS). Studies assessing myocardial fibrosis in relation to these manifestations are scarce. This cross-sectional, single-center study assessed ventricular volumes, ventricular function, and myocardial fibrosis by cardiac magnetic resonance imaging (CMR) in patients with MFS harboring a (likely) pathogenic FBN1 variant. The presence and extent of fibrosis were assessed by late gadolinium enhancement (LGE) and extracellular volume measurement (ECV). Data on 24-h Holter monitoring and clinical data were extracted from electronic patient records. The study included 32 unselected patients with MFS (median age 38 years [range 10-69], 41% women). No focal myocardial fibrosis was detected. Six patients (21%) had diffuse fibrosis (ECV > 29%). No association was found between the presence of diffuse fibrosis and clinically relevant myocardial dysfunction. Five patients (16%) had reduced left ventricular ejection fraction (LVEF < 55%). While all of these exhibited mitral annular disjunction (MAD), only two had ECV > 29%. Patients with MAD had increased indexed LV volumes (median end-diastolic volume, 92 mL/m2 [IQR, 78-100] vs. 78 mL/m2 [IQR, 71-87]; median end-systolic volume, 31 mL/m2 [IQR, 23-46] vs. 22 mL/m2 [IQR, 21-28]), also after adjusting for the presence of mitral and aortic valve regurgitation. No differences in ECV were seen between patients with and without MAD. In this cohort of patients with MFS, focal myocardial fibrosis was not detected using CMR. Although diffuse fibrosis was observed in 21% of patients, no evident connection to clinically relevant myocardial dysfunction was found. Further studies should evaluate the impact of diffuse fibrosis on clinical outcome prediction.

Exome sequencing identifies a novel FBN1 variant in a Chinese family with Marfan syndrome that includes aberrant right subclavian artery

Abstract Background Marfan syndrome (MFS) is an inherited autosomal dominant disorder that affects connective tissue with an incidence of about 1 in 5,000 to 10,000 people. Ninety percent of MFS is caused by mutations in the fibrillin-1 (fbn1) gene. We recruited a family with MFS phenotype in South China and identified a novel variant in fbn1 by whole exome sequencing (WES). The zebrafish share high genetic similarity to humans. This study aimed to generate this novel mutation in the fbn1 gene of zebrafish using the CRISPR/Cas9 technology and researched whether this variant is pathogenic. Methods A three-generation consanguineous family was recruited in this study, which was visited and interviewed for the clinical data and family history. Peripheral blood samples were collected from family members for DNA isolation and WES. The 3D structure of the protein was predicted by Alphafold. CRISPR/Cas9 was applied to generate an fbn1 nonsense mutation (fbn1+/−) in zebrafish. Morphological abnormalities were assessed in F2 fbn1+/− zebrafish by comparing with the wild-type (WT) controls at different development stages. Results Our study recruited a family with MFS phenotype in South China and identified a novel variant [NM_000138.5; c.7764C&amp;gt;G: p.(Y2588*)] in fbn1. Through Sanger sequencing, we found that family members Ⅲ-1 (son) and Ⅲ-2 (daughter) had the fbn1 variant segregated with MFS in the family. The p.Y2588* mutation resulted in the absence of 283 amino acids, thereby leading to the deficiency of 17 β-folded structures, 4 α-helix structures, and various loop structures. Compared with WT zebrafish, F2 fbn1+/− zebrafish exhibited aortic arches bleeding, abnormal angiogenesis, decreased cardiac volume, cardiac function defects, curly tail, and cartilage malformations. Conclusion A novel variant [NM_000138.5; c.7764C&amp;gt;G: p.(Y2588*)] was identified in fbn1 gene, which has not been reported in previous literature. The variant caused loss of function through premature protein truncation or nonsense-mediated mRNA decay. In zebrafish, we identified functional evidence of the detected nonsense mutation, which aligns with the clinical significance, suggesting a pathogenic variant of fbn1. Zebrafish as a novel, efficient tool to allow for the quick classification of unknown variants in fbn1 and improve the clinical diagnosis and treatment of MFS. It has brought the implementation of personal and precision medicine in the clinic within reach and made it possible to find patient-specific treatments.Marfanoid symptoms of the patient.Phenotypic Spectrum of fbn1+/− Zebrafish

Dinucleotide composition representation -based deep learning to predict scoliosis-associated Fibrillin-1 genotypes.

Scoliosis is a pathological spine structure deformation, predominantly classified as "idiopathic" due to its unknown etiology. However, it has been suggested that scoliosis may be linked to polygenic backgrounds. It is crucial to identify potential Adolescent Idiopathic Scoliosis (AIS)-related genetic backgrounds before scoliosis onset. The present study was designed to intelligently parse, decompose and predict AIS-related variants in ClinVar database. Possible AIS-related variant records downloaded from ClinVar were parsed for various labels, decomposed for Dinucleotide Compositional Representation (DCR) and other traits, screened for high-risk genes with statistical analysis, and then learned intelligently with deep learning to predict high-risk AIS genotypes. Results demonstrated that the present framework is composed of all technical sections of data parsing, scoliosis genotyping, genome encoding, machine learning (ML)/deep learning (DL) and scoliosis genotype predicting. 58,000 scoliosis-related records were automatically parsed and statistically analyzed for high-risk genes and genotypes, such as FBN1, LAMA2 and SPG11. All variant genes were decomposed for DCR and other traits. Unsupervised ML indicated marked inter-group separation and intra-group clustering of the DCR of FBN1, LAMA2 or SPG11 for the five types of variants (Pathogenic, Pathogeniclikely, Benign, Benignlikely and Uncertain). A FBN1 DCR-based Convolutional Neural Network (CNN) was trained for Pathogenic and Benign/ Benignlikely variants performed accurately on validation data and predicted 179 high-risk scoliosis variants. The trained predictor was interpretable for the similar distribution of variant types and variant locations within 2D structure units in the predicted 3D structure of FBN1. In summary, scoliosis risk is predictable by deep learning based on genomic decomposed features of DCR. DCR-based classifier has predicted more scoliosis risk FBN1 variants in ClinVar database. DCR-based models would be promising for genotype-to-phenotype prediction for more disease types.

Intrinsic cardiomyopathy in pediatric Marfan syndrome: predictive factors and risk assessments.

Marfan syndrome (MFS) is associated with cardiovascular complications, particularly valvulopathies; however, its association with primary cardiomyopathy remains unclear. This retrospective cohort study examined the cardiomyopathy characteristics (CMCs) in pediatric patients with MFS. CMCs were defined as meeting at least one of the following echocardiography or clinical parameters: (1) cardiac index (CI) too low for patient's age, (2) ejection fraction (EF) <50%, and (3) diastolic dysfunction. The predictive factors for CMCs were determined using a multivariable logistic regression model. Among 83 patients with MFS (age, median [range], 12.5 [0.4-22.3] years), 39.8% exhibited CMCs. Only 4 patients (5%) showed heart failure symptoms (NYHA > 1). Independent predictors for CMCs included a systemic score of ≥7 (revised Ghent criteria) and likely pathogenic or pathogenic variants in FBN1, including variants that introduce a premature stop codon, splice site variants, and missense variants involving cysteine. A multivariable score was constructed with an AUC of 0.733. This study offers valuable insights into the prevalence and predictors of CMC in pediatric patients with MFS and presents potential strategies for risk assessment of cardiomyopathy. The objective of this study was to elucidate the contentious issue of intrinsic cardiomyopathy in Marfan syndrome and demonstrate its notable occurrence even in pediatric patients who do not exhibit heart failure symptoms or valvular complications. We highlighted the importance of specific FBN1 variants and higher systemic scores in identifying the potential for intrinsic cardiomyopathy in pediatric patients with Marfan syndrome.

A Novel Heterozygous Intronic FBN1 Variant Contributes to Aberrant RNA Splicing in Marfan Syndrome.

Marfan syndrome (MFS) is a complex genetic systemic connective tissue disorder. It is well known that genetic factors play a critical role in the progression of MFS, with nearly all cases attributed to variants in the FBN1 gene. We investigated a Chinese family with MFS spanning two generations. Whole exome sequencing, in silico analysis, minigene constructs, transfection, RT-PCR, and protein secondary structure analysis were used to analyze the genotype of the proband and his father. The main clinical manifestations of the proband and his father were subluxation of the left lens and high myopia with pectus deformity. Whole exome sequencing identified a novel single nucleotide variant (SNV) in the FBN1 gene at a non-canonical splice site, c.443-3C>G. This variant resulted in two abnormal mRNA transcripts, leading to a frameshift and an in-frame insertion. Further invitro experiments indicated that the c.443-3C>G variant in FBN1 was pathogenic and functionally harmful. This research identified a novel intronic pathogenic FBN1: c.443-3C>G gene variant, which led to two different aberrant splicing effects. Further functional analysis expands the variant spectrum and provides a strong indication and sufficient basis for preimplantation genetic testing for monogenic disease (PGT-M).

Late diagnosis of Marfan syndrome is associated with unplanned aortic surgery and cardiovascular death

BackgroundMarfan syndrome (MFS) guidelines recommend optimal pharmacologic therapy (OPT) and replacement of the ascending aorta (RAA) at 5.0 cm in diameter to prevent acute type A aortic dissection (ATAAD) and death. The effect of early MFS diagnosis and initiation of therapy on outcomes is not known. Therefore, we sought to evaluate the effect of age at MFS diagnosis and therapy initiation on delayed RAA and death. MethodsThis retrospective observational cohort study with long-term follow-up included consecutive patients with MFS, pathogenic FBN1 variant, and regular visits to a European Reference Network Center. We considered MFS diagnosis at age ≥21 years late and OPT initiation at age <21 years early. Outcomes were delayed RAA with aneurysm diameter >5.0 cm or ATAAD and death from all causes. We used landmark design starting at age 21 years to determine associations with outcomes. ResultsThe study group consisted of 288 patients (45.1% male), including 169 patients with late diagnosis of MFS (58.7%) and 63 with early OPT (21.9%). During mean follow-up of 25 ± 14.7 years, 78 patients had delayed RAA, with 42 operations for ATAAD and 36 for aneurysms ≥5.0 cm. There were 33 deaths, including 11 deaths late after ATAAD. All deaths were cardiovascular. Late diagnosis, but not early OPT, showed univariate association with delayed RAA (P < .001) and death (P = .025). Multivariate Cox regression analysis confirmed late diagnosis as predictor of delayed RAA (hazard ratio, 8.01; 95% confidence interval, 2.52-25.45; P < .001) and death (hazard ratio, 4.68; 95% confidence interval, 1.17-18.80; P = .029). ConclusionsLate diagnosis of MFS is associated with delayed surgery and death.

Mitral annular disjunction and its progression during childhood in Marfan syndrome.

Data on mitral annular disjunction (MAD) in children with Marfan syndrome (MFS) are sparse. To investigate the diagnostic yield of MAD by echocardiography and cardiac magnetic resonance imaging (CMR), its prevalence and progression during childhood. We included patients <21 years old with MFS, defined by 2010 Ghent criteria and a pathogenic FBN1 variant or ectopia lentis. Two readers measured systolic separation between the mitral valve (MV) posterior hinge point and left ventricular (LV) myocardium on initial and subsequent imaging. MAD was defined as MV-LV separation ≥2 mm, MV prolapse (MVP) as atrial displacement ≥2 mm. Kappa coefficients evaluated echocardiogram-CMR agreement. Bland-Altman and intraclass correlation coefficients (ICCs) assessed inter-rater and inter-modality reliability. Univariable mixed-effects linear regression was used to evaluate longitudinal changes of MAD. MAD was detected in 60% (110/185) eligible patients. MVP was present in 48% (53/110) of MAD and MAD in 90% (53/59) of MVP. MAD detection by CMR and echocardiography had 96% overall agreement (Kappa = 0.89, P < 0.001) and a 0.32 mm estimate bias (95% CI 0.00, 0.65). ICC by echocardiography, CMR, and between modalities were 0.97 (95% CI 0.93, 0.98), 0.92 (95% CI 0.79, 0.97), and 0.91 (95% CI 0.85, 0.94), respectively. MAD was associated with aortic root dilation (P < 0.001). MAD was found in children of all ages, increased +0.18 mm/year (95% CI +0.14, +0.22) during a median duration of 5.5 years (IQR 3.1, 7.5 years). MAD indexed by height yielded a constant value +0.0002 mm/m/year (95% CI -0.0002, +0.0005 mm/m/year). MAD was common in pediatric MFS and was associated with aortic root dilation. MAD detection by echocardiography and CMR was highly reliable, suggesting that routine assessment in MFS is feasible. MAD was present in neonates and progressed over time but remained constant when indexing by height. Further studies are needed to evaluate MAD as a biomarker for clinical outcomes in pediatric MFS.

Genotype and clinical phenotype of children with Marfan syndrome in Southeastern Anatolia

The cardinal phenotypic hallmarks of Marfan syndrome (MFS) include cardiac, ocular, and skeletal abnormalities. Since the clinical phenotype of MFS is highly heterogeneous, with certain symptoms appearing as children age, the diagnostic process and establishing a genotype-phenotype association in childhood MFS can be challenging. The lack of sufficient childhood studies also makes it difficult to interpret the subject. This study aims to evaluate the relationship between clinical symptoms used as diagnostic criteria and FBN1 variations in children with MFS. This study investigated the relationships between genotypes and phenotypes in 131 children suspected of having Marfan syndrome (MFS). Diagnosis of MFS was made according to the revised Ghent nosology. FBN1 variants were categorized based on exon regions, type of variant, and pathogenicity classes. These FBN1 variants were then correlated with the clinical manifestations including cardiovascular, ocular, facial, and skeletal abnormalities. Out of the children, 43 were diagnosed with MFS. FBN1 variant was identified in 32 (74.4%) of the MFS children. MFS diagnosis could not be made in five (15.6%) FBN1 variant-positive children. The most common cardinal finding is cardiac anomalies n = 38 (88.3%). The most common FBN1 pathogenic variant was c.1786 T > C/p.Cys596Arg n = 4 (12.5%). The distribution of pathogenic variants was as follows: 29 (90.6%) missense, 2 (6.3%) frameshift, and 1 (3.1%) nonsense. The numbers of AD and EL of the variant-positive children were 16 (50%) and 14 (43.7%), respectively. Ocular abnormalities were more common in children with FBN1-positive MFS (p = 0.009). There was no difference in the number of cardiac abnormalities between FBN1-positive and FBN1-negative MFS patients (p = 0.139). Conclusion: This study examines the relationship between FBN1 variants and clinical features used as diagnostic criteria in MFS children. The findings emphasize the importance of long-term monitoring of heterogeneous clinical phenotypes and bioinformatic reanalysis in determining the genotype-phenotype relationship in children, as MFS symptoms can vary with age.What is Known:• Marfan syndrome has highly variable phenotypic heterogeneity.• The genotype-phenotype relationship in childhood Marfan syndrome is not clear enough due to the variation in the time of onset of the findings.What is New:• This article provides regional data for the field of research on genotype-phenotype relationships in childhood Marfan syndrome.• Long-term follow-up of clinical findings and bioinformatics reanalysis is an important requirement for a well-established genotype-phenotype relationship in childhood Marfan syndrome.

Quantitative measurement of dural ectasia: associations with clinical and genetic characteristics in Marfan syndrome.

Dural ectasia (DE) may significantly impact Marfan syndrome (MFS) patients' quality of life due to chronic lower back pain, postural headache and urinary disorders. We aimed to evaluate the association of quantitative measurements of DE, and their evolution over time, with demographic, clinical and genetic characteristics in a cohort of MFS patients. We retrospectively included 88 consecutive patients (39% females, mean age 37.1 ± 14.2 years) with genetically confirmed MFS who underwent at least one MRI or CT examination of the lumbosacral spine. Vertebral scalloping (VS) and dural sac ratio (DSR) were calculated from L3 to S3. Likely pathogenic or pathogenic FBN1 variants were categorized as either protein-truncating or in-frame. The latter were further classified according to their impact on the cysteine content of fibrillin-1. Higher values of the systemic score (revised Ghent criteria) were associated with greater DSR at lumbar (p < 0.001) and sacral (p = 0.021) levels. Patients with protein-truncating variants exhibited a greater annual increase in lumbar (p = 0.039) and sacral (p = 0.048) DSR. Mutations affecting fibrillin-1 cysteine content were linked to higher VS (p = 0.009) and DSR (p = 0.038) at S1, along with a faster increase in VS (p = 0.032) and DSR (p = 0.001) in the lumbar region. Our study shed further light on the relationship between genotype, dural pathology, and the overall clinical spectrum of MFS. The identification of protein-truncating variants and those impacting cysteine content may therefore suggest closer patient monitoring, in order to address potential complications associated with DE.

TGFβ level in healthy and children with Marfan syndrome-effective reduction under sartan therapy.

Transforming growth factor β (TGFβ) metabolism plays an important role in the pathogenesis of Marfan syndrome (MFS). Accordingly, drug therapy uses TGFβ receptor blockade to slow down the cardiovascular manifestations, above all aortic root dilatation. Angiotensin II type 1 receptor blockers (ARBs) have been shown to reduce TGFβ levels in adults. Data on childhood are lacking and are now being investigated in the TiGer For Kids study presented here. We examined 125 children without chronic disease and 31 pediatric Marfan patients with a proven FBN1 variant with regard to TGFβ levels. In addition, we measured TGFβ levels during the initiation of ARB therapy in pediatric Marfan patients. In children without chronic disease, TGFβ levels were found to decrease from childhood to adolescence (p < 0.0125). We could not measure a relevantly increased TGFβ level in pediatric Marfan patients. However, we showed a significant suppression of the TGFβ level after treatment with ARBs (p < 0.0125) and a renewed increase shortly before the next dose. The TGFβ level in childhood changes in an age-dependent manner and decreases with age. The TGFβ level drops significantly after taking ARBs. Based on our experience and data, a TGFβ receptor blockade in childhood seems reasonable. So far, TGFβ level cannot be used as an MFS screening biomarker.

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.

Exploring a Transcriptome-forward Approach for Genetic Evaluation in Thoracic Aortopathy

Background/Objective: Thoracic aortic aneurysm (TAA) is an aortopathy that predisposes to aortic dissection and rupture. Transcriptomic analysis has diagnostic utility in other diseases, but this has not been developed for TAA. We therefore sought to implement the Genome Analysis Toolkit (GATK) as a tool for high-throughput detection of novel variants in RNA sequencing (RNA-seq) data from patients with TAA.&#x0D; Methods: Human proximal aortic tissue samples from 63 TAA patients and 15 controls were used to establish primary smooth muscle cell (SMC) lines in culture. Total RNA was extracted at early passage; RNA-seq was performed using 150 base pair paired-end reads. Variants were called from RNA-seq reads using the GATK’s HaplotypeCaller tool. The MarkDuplicates tool tagged duplicate reads, but these were retained for variant analysis. Singletons were defined as heterozygous variants unique to one sample in the overall group.&#x0D; Results: The RNA-seq pipeline was validated by confirming known mutations in 2 patients, inspecting reads directly in the Integrative Genomics Viewer (IGV), and genotyping for a common single nucleotide polymorphism. Across all 78 samples, the GATK pipeline identified 4,823,462 variant sites, 236,495 of which were in coding regions. Variant sites were filtered for those located within the coding regions of 31 genes curated for known evidence of aortic disease causality. Among the 511 coding variant sites in these genes, 330 single nucleotide variants and 33 insertions/deletions were identified as singletons. Singleton variant calls were evaluated for quality and annotated in order to predict their likelihood of pathogenicity, thus far identifying strong candidate causal variants in FBN1, TGFBR1, TGFB3, GATA4, and HEY2.&#x0D; Conclusion: Application of the GATK RNA-seq pipeline expands our prior IGV analysis, further demonstrating the potential diagnostic utility of transcriptomic analysis of aortic SMCs in TAA.&#x0D; Scientific Impact: Identifying novel aortopathy-associated variants could improve future disease detection and prediction of severity.

Clinical and Genetic Landscape of Ectopia Lentis Based on a Cohort of Patients From 156 Families.

To extend the mutation spectrum and explore the characteristics of genotypes and ocular phenotypes in ectopia lentis (EL). Variants in all 14 reported EL-associated genes were selected from in-house data sets as well as literature review, and available clinical data were analyzed. Likely pathogenic variants in three genes were identified in 156 unrelated families with EL from the in-house cohort, of which 97.4% resulted from variants in FBN1, whereas the remaining were caused by variants in ADAMTSL4 (1.3%) and LTBP2 (1.3%). A comparative analysis of the in-house data and literature review suggested several characteristics: (1) a higher proportion of cysteine involvement variants in FBN1, either variants introducing or eliminating cysteine, and an earlier diagnosis age were presented in our cohort than in published literature; (2) the axial length (AL) and refractive error increased more rapidly with age in preschool EL children than normal children, and the increased rate of AL was slower in patients with surgery than those without surgery; (3) aberrant astigmatism was common in EL; and (4) worse vision and earlier onset age were observed in patients with non-FBN1 variants (all P < 0.05). Variants in FBN1 are the predominant cause of EL, with the most common cysteine involvement variants. Early-stage EL manifests refractive error but gradually converts to axial myopia through defocus introduced by lens dislocation. Aberrant astigmatism is a suggestive sign of EL. Non-FBN1 variants cause early-onset and severe phenotypes. These results provide evidence for early diagnosis as well as timely treatment for EL.

The Fbn1 gene variant governs passive ascending aortic mechanics in the mgΔlpn mouse model of Marfan syndrome when superimposed to perlecan haploinsufficiency.

Ascending thoracic aortic aneurysms arise from pathological tissue remodeling that leads to abnormal wall dilation and increases the risk of fatal dissection/rupture. Large variability in disease manifestations across family members who carry a causative genetic variant for thoracic aortic aneurysms suggests that genetic modifiers may exacerbate clinical outcomes. Decreased perlecan expression in the aorta of mgΔlpn mice with severe Marfan syndrome phenotype advocates for exploring perlecan-encoding Hspg2 as a candidate modifier gene. To determine the effect of concurrent Hspg2 and Fbn1 mutations on the progression of thoracic aortopathy, we characterized the microstructure and passive mechanical response of the ascending thoracic aorta in female mice of four genetic backgrounds: wild-type, heterozygous with a mutation in the Fbn1 gene (mgΔlpn), heterozygous with a mutation in the Hspg2 gene (Hspg2+/-), and double mutants carrying both the Fbn1 and Hspg2 variants (dMut). Elastic fiber fragmentation and medial disarray progress from the internal elastic lamina outward as the ascending thoracic aorta dilates in mgΔlpn and dMut mice. Concurrent increase in total collagen content relative to elastin reduces energy storage capacity and cyclic distensibility of aortic tissues from mice that carry the Fbn1 variant. Inherent circumferential tissue stiffening strongly correlates with the severity of aortic dilatation in mgΔlpn and dMut mice. Perlecan haploinsufficiency superimposed to the mgΔlpn mutation curbs the viability of dMut mice, increases the occurrence of aortic enlargement, and reduces the axial stretch in aortic tissues. Overall, our findings show that dMut mice are more vulnerable than mgΔlpn mice without an Hspg2 mutation, yet later endpoints and additional structural and functional readouts are needed to identify causative mechanisms.

Genetic testing and diagnostic strategies of fetal skeletal dysplasia: a preliminary study in Wuhan, China

BackgroundFetal skeletal dysplasia is a diverse group of degenerative diseases of bone and cartilage disorders that can lead to movement disorder and even death. This study aims to evaluate the diagnostic yield of sonographic examination and genetic testing for fetal skeletal dysplasia.MethodsFrom September 2015 to April 2021, the study investigated 24 cases with suspected short-limb fetuses, which were obtained from Tongji Hospital affiliated to Tongji Medical College of Huazhong University of Science and Technology. To identify the causative gene, multiple approaches (including karyotype analysis, copy number variations and whole exome sequencing) were performed on these fetuses. And further segregation analysis of the candidate variant was performed in parents by using Sanger sequencing.Results① Out of 24 cases, likely pathogenic variants in FGFR3, FBN2, COL1A2, CUL7 and DYNC2H1 were detected in 6 cases; pathogenic variants in FGFR3, IMPAD1 and GORAB were identified in other 6 cases; and variants in WNT1, FBN1, OBSL1, COL1A1, DYNC2H1 and NEK1, known as Variant of Undetermined Significance, were found in 4 cases. There were no variants detected in the rest 8 cases by the whole exome sequencing. ② Of 24 cases, 12 (50%) were found to carry variants (pathogenic or likely pathogenic) in seven genes with 12 variants. Four fetuses (16.7%) had variants of uncertain significance.ConclusionGenetic testing combining with ultrasound scanning enhances the accurate diagnosis of fatal skeletal dysplasia in utero, and then provides appropriate genetic counseling.

Is Marfan Syndrome Associated with Primary Structural Changes in the Left Atrium?

Marfan syndrome (MFS) is an autosomal-dominant multisystem connective tissue disorder that is based on mutations in the FBN1 gene and variably affects different organs, including the heart. In this study, we investigated cardiac function with a focus on the left atrium (LA) in a relatively large cohort of patients with MFS. After screening of 1165 patients that had been examined in our center between 2016 and 2020, 231 adult MFS patients with and without aortic operation were included in our study and compared to a healthy control group (n = 106). Cardiac function was assessed by transthoracic echocardiography and NT-proBNP was used as a secretory marker. Most (94.8%) of the patients received genetic testing. Left ventricular function was within normal ranges and not impaired. Interestingly, we found that LA size and secretory activity were increased in MFS patients, despite normal left ventricular filling pressures. This finding was even more pronounced in MFS patients with prior aortic surgery. A correlation between LA size or NT-proBNP levels and the type of pathogenic FBN1 variant could not be identified. Right ventricular function and right atrial size were increased only in MFS patients that had undergone aortic surgery. In conclusion, these findings suggest that MFS leads to structural changes in the LA that are not solely resulting from left ventricular dysfunction, but probably can be considered a primary pathology of MFS.

Re-evaluation of a Fibrillin-1 Gene Variant of Uncertain Significance Using the ClinGen Guidelines.

Marfan syndrome (MFS) is caused by fibrillin-1 gene (FBN1) variants. Mutational hotspots and/or well-established critical functional domains of FBN1 include cysteine residues, calcium-binding consensus sequences, and amino acids related to interdomain packaging. Previous guidelines for variant interpretation do not reflect the features of genes or related diseases. Using the Clinical Genome Resource (ClinGen) FBN1 variant curation expert panel (VCEP), we re-evaluated FBN1 germline variants reported as variants of uncertain significance (VUSs). We re-evaluated 26 VUSs in FBN1 reported in 161 patients with MFS. We checked the variants in the Human Genome Mutation Database, ClinVar, and VarSome databases and assessed their allele frequencies using the gnomAD database. Patients' clinical information was reviewed. Four missense variants affecting cysteines (c.460T>C, c.1006T>C, c.5330G>C, and c.8020T>C) were reclassified as likely pathogenic and were assigned PM1_strong or PM1. Two intronic variants were reclassified as benign by granting BA1 (stand-alone). Four missense variants were reclassified as likely benign. BP5 criteria were applied in cases with an alternate molecular basis for disease, one of which (c.7231G>A) was discovered alongside a pathogenic de novo COL3A1 variant (c.1988G>T, p.Gly633Val). Considering the high penetrance of FBN1 variants and clinical variability of MFS, the detection of pathogenic variants is important. The ClinGen FBN1 VCEP encompasses mutational hotspots and/or well-established critical functional domains and adjusts the criteria specifically for MFS; therefore, it is beneficial not only for identifying pathogenic FBN1 variants but also for distinguishing these variants from those that cause other connective tissue disorders with overlapping clinical features.

Weill-Marchesani syndrome: natural history and genotype-phenotype correlations from 18 news cases and review of literature

BackgroundWeill-Marchesani syndrome (WMS) belongs to the group of acromelic dysplasias, defined by short stature, brachydactyly and joint limitations. WMS is characterised by specific ophthalmological abnormalities, although cardiovascular defects have also...