FBN1 Variants Research Articles

Multi-Omics Profiling in Marfan Syndrome: Further Insights into the Molecular Mechanisms Involved in Aortic Disease.

Thoracic aortic aneurysm is a potentially life-threatening disease with a strong genetic contribution. Despite identification of multiple genes involved in aneurysm formation, little is known about the specific underlying mechanisms that drive the pathological changes in the aortic wall. The aim of our study was to unravel the molecular mechanisms underlying aneurysm formation in Marfan syndrome (MFS). We collected aortic wall samples from FBN1 variant-positive MFS patients (n = 6) and healthy donor hearts (n = 5). Messenger RNA (mRNA) expression levels were measured by RNA sequencing and compared between MFS patients and controls, and between haploinsufficient (HI) and dominant negative (DN) FBN1 variants. Immunohistochemical staining, proteomics and cellular respiration experiments were used to confirm our findings. FBN1 mRNA expression levels were highly variable in MFS patients and did not significantly differ from controls. Moreover, we did not identify a distinctive TGF-β gene expression signature in MFS patients. On the contrary, differential gene and protein expression analysis, as well as vascular smooth muscle cell respiration measurements, pointed toward inflammation and mitochondrial dysfunction. Our findings confirm that inflammatory and mitochondrial pathways play important roles in the pathophysiological processes underlying MFS-related aortic disease, providing new therapeutic options.

A systematic study of mosaicism in heritable thoracic aortic aneurysm and dissection

Mosaicisms are often overlooked in routine molecular diagnosis. Although not common, they are of great significance for accurate diagnosis and genetic counseling. In this study, we systematically evaluated the frequency of mosaicisms in both asymptomatic parents and affected patients with thoracic aortic aneurysm and dissection (TAAD). Next-generation sequencing (NGS) data from 1085 patients was reanalyzed with a more lenient allele frequency to detect potential mosaic variants. In addition, parental mosaicisms were investigated in 80 TAAD families. Finally, a total of six mosaic variants were detected in our cohort. Three of them were identified in symptomatic patients and three were in asymptomatic parents. Notably, a low-level mosaic variant in TGFB2 was detected combined with a causative FBN1 variant in patient AD2001, which might partially explain the clinical heterogeneity in his family. Our study hinted that it is necessary and feasible to implement mosaicism analysis in routine molecular diagnosis.

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

Background: The lifespan of Marfan Syndrome (MFS) patients is shortened, especially in patients without early diagnostics, preventive treatment, and elective surgery. Clinically, MFS diagnosis is mainly dependent on phenotypes, but for children, sporadic cases, or suspicious MFS patients, molecular genetic testing, and mainly FBN1 mutation screening, plays a significant role in the diagnosis of MFS. PGT-M gives couples that had a family history of monogenic disorders the opportunity to avoid the occurrence of MFS. Methods: In this study, 11 families with MFS were recruited and complete clinical features were collected. Variants were classified and interpreted through pedigree analysis according to guidelines. Two families chose to undergo PGT-M; 16 blastocysts were biopsied and amplified. Haplotype analysis was performed to deduce the embryo’s genotype by using single nucleotide polymorphisms (SNPs) identified in each sample. Results: We identified 11 potential disease-causing FBN1 variants, six of which are novel. All variants were assessed with prediction tools to assess mutation pathogenicity, population databases to evaluate population allele frequency, literature databases to identify whether the variant had been reported in MFS patients, and multiple sequence alignment to carry out conservative analysis. Finally, nine variants were classified as likely pathogenic/pathogenic variants. Among 11 variants, eight variants were missense, and seven of them were located in the Ca-binding EGF-like motifs, moreover, half of them substituted conserved Cysteine residues. We also identified a splice site variant, a frameshift variant, and a synonymous variant. There are two variants that are de novo variants. PGT-M helped two MFS families give birth to a healthy baby not carrying the FBN1 mutation. Conclusions: In the present study, the FBN1 mutation spectrum was enriched, and may help further elucidate the pathogenesis, benefiting clinical diagnosis and management of MFS. We make use of a reliable PGT-M method for the successful birth of healthy babies to two MFS families.

Arrhythmia and cardiomyopathy in Heritable Thoracic Aortic Disease: an international retrospective cohort study

Abstract Background Marfan syndrome (MFS), Loeys-Dietz syndrome (LDS) and related heritable thoracic aortic diseases (HTAD) are well-known for their aortic complications. Myocardial dysfunction and arrhythmia are less known in this setting but have been increasingly reported as additional causes of morbidity and mortality. Related to the rarity of the disorders, data on the prevalence of these features and clinical characteristics of the patients are difficult to obtain, calling for a multicentre initiative. Purpose To study the prevalence of myocardial dysfunction and arrhythmia in patients with HTAD and describe their clinical and genetic profile. Methods Nine centres from seven countries participated in this multicentre retrospective study. Medical records of patients 12 years or older carrying a (likely) pathogenic variant in the FBN1 gene, LDS genes (TGFBR1, TGFBR2, TGFB2, TGFB3 and SMAD3) or ACTA2 gene were screened. Patients presenting myocardial dysfunction and/or arrhythmia were identified, and clinical and genetic data were collected. Myocardial dysfunction included (a)symptomatic reduced ejection fraction (EF <50% – HFrEF) or symptomatic preserved EF (HFpEF), as documented in the patient charts. Arrhythmias included atrial fibrillation or flutter (AF/AFL), ventricular tachycardia (VT), ventricular fibrillation (VF) and (aborted) sudden cardiac death (SCD) (presumed arrhythmogenic). Results In total, 3219 patients with HTAD were screened: 2761 with a variant in FBN1, 385 with a variant in one of the LDS genes (TGFBR1, TGFBR2, TGFB2, TGFB3 and SMAD3) and 73 carrying a variant in ACTA2. Myocardial dysfunction and arrhythmia were not reported in patients carrying an ACTA2 variant. Myocardial dysfunction was observed in patients with a variant in FBN1 and the LDS genes, without significant differences in prevalence (2.3% vs. 1.8%, p=0.563). Patients with a variant in the LDS genes presenting myocardial dysfunction were younger than patients carrying a variant in FBN1 (25±11 years vs. 39±17 years, p=0.034). The prevalence of VT/VF/SCD was similar in patients with a variant in one of the LDS genes compared to those with a variant in FBN1 (1.6% vs. 0.8%, p=0.132) and there was no difference in age at time of event (26±13 years vs. 33±14 years, p=0.289). Among patients with a variant in the LDS genes, the prevalence of VT/VF/SCD was highest in patients carrying a variant in the TGFBR2 gene and was significantly higher compared to patients with a variant in FBN1 (3.4% vs. 0.8%, p=0.017). In contrast, AF/AFL was significantly more often reported in patients with a variant in FBN1 compared to those with a variant in one of the LDS genes (1.7% vs. 0.3%, p=0.033). Conclusions Myocardial dysfunction and arrhythmia are rare features in patients with HTAD. They occur predominantly in patients with a variant in FBN1 and LDS genes, but were not reported in patients carrying a variant in the ACTA2 gene. Further analysis to identify other contributing factors is necessary. Funding Acknowledgement Type of funding sources: None. Figure 1

Genotype-phenotype correlations in Marfan syndrome patients with FBN1 mutations: a cohort study on 1575 patients

Abstract Background Marfan syndrome (MFS) is a connective tissue disorder in which several systems are affected with great phenotypic variability. Although known to be associated with pathogenic variants in the FBN1 gene, few genotype-phenotype correlations have been found in probands' studies only. Purpose The aim of this study is to provide survival curves and genotype-phenotype correlations in all patients with FBN1 mutations, probands and relatives. Methods We established survival curves and sought genotype–phenotype correlations in a population of 1575 consecutive MFS patients with pathogenic class 4 or 5 variants in the FBN1 gene. This population represents the most comprehensive clinical database worldwide on MFS. Results Global survival was 90% at 60 years. However, lifelong aortic event rate (either dissection or surgery) and survival were impacted by the genotype. Premature termination codons (PTC), resulting in haploinsufficiency, were associated with a shorter life expectancy and a high lifelong risk of an aortic event (83%). Interestingly, these variants were also associated with the highest risk of severe scoliosis (52%) and with a lower risk for ectopia lentis (EL) surgery (13%). Dominant negative in-frame pathogenic variants could be subdivided according to their impact on the cysteine content of fibrillin-1: cysteine loss (–Cys) was associated with high aortic risk (73%) and a higher frequency of EL surgery (43%); cysteine addition was associated with moderate aortic risk (29%) and the highest frequency of EL surgery (48%); unchanged cysteine content was associated with high aortic risk (61%) and lower frequency of EL surgery (23%). No gene-region effect was observed, except for a more severe phenotype for in-frame variants with cysteine loss within the “neonatal region”. Aortic risk was greater for males in all subgroups, and probands were more severely affected. Conclusions MFS genotype-phenotype correlations related to pathogenic FBN1 variants exist for aortic and extra-aortic features. This leads us to propose new tools to refine the prognosis in this population. Preventive therapy with β-blockers and restricted exercise should be proposed regardless of the aortic diameter in the high aortic risk groups (PTC and –Cys variants). These results have major consequences on genetic counseling and personalized medicine for patients carrying a FBN1 mutation. This study also improves the overall understanding of the role of FBN1 in various organs. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): Fondation Coeur et Recherche, Paris, FranceFédération Française de Cardiologie, Paris, France Patients with PTC vs. in-frame mutationsDifferences within in-frame mutations

Marfan syndrome.

Marfan syndrome (MFS) is an autosomal dominant, age-related but highly penetrant condition with substantial intrafamilial and interfamilial variability. MFS is caused by pathogenetic variants in FBN1, which encodes fibrillin-1, a major structural component of the extracellular matrix that provides support to connective tissues, particularly in arteries, the pericondrium and structures in the eye. Up to 25% of individuals with MFS have de novo variants. The most prominent manifestations of MFS are asymptomatic aortic root aneurysms, aortic dissections, dislocation of the ocular lens (ectopia lentis) and skeletal abnormalities that are characterized by overgrowth of the long bones. MFS is diagnosed based on the Ghent II nosology; genetic testing confirming the presence of a FBN1 pathogenetic variant is not always required for diagnosis but can help distinguish MFS from other heritable thoracic aortic disease syndromes that can present with skeletal features similar to those in MFS. Untreated aortic root aneurysms can progress to life-threatening acute aortic dissections. Management of MFS requires medical therapy to slow the rate of growth of aneurysms and decrease the risk of dissection. Routine surveillance with imaging techniques such as transthoracic echocardiography, CT or MRI is necessary to monitor aneurysm growth and determine when to perform prophylactic repair surgery to prevent an acute aortic dissection.

Impact of genotype on the progression of aortic disease in patients with Marfan syndrome and Loeys–Dietz syndrome

Marfan and Loeys–Dietz syndromes are connective tissue disorders characterized by high clinical variability. The major morbidity and mortality in both syndromes relate to the dilatation of the aorta predisposing to aortic tear. We investigated the putative relationship between the genotype, aortic growth speed and the occurrence of severe cardio vascular events (prophylactic surgery of the aortic root, aortic dissection or related death). We have performed a retrospective study of 102 patients with pathogenic variants in FBN1 , TGFβR1 and R2 and SMAD3 genes followed at a Marfan reference center in France. The average age at the start of the study was 13.8 years and data were collected over 5 years. The FBN1 variants were classified as haploinsufficient (HI) or dominant negative (DN). Aortic diameters and aortic dilatation at the level of the Valsalva sinuses were assessed by echocardiography. No overall aortic growth difference was found between Marfan and Loeys–Dietz syndrome (1.14 vs. 1.11 mm/year, P = 0.74), neither between HI and DN groups (1.12 vs. 1.01 mm/year, P = 0.36). However, patients with a SMAD 3 mutation seem to have lower aortic growth than those in the TGFβ group (0.91 vs. 1.34 mm/year, P = 0.36). No difference concerning Valsalva sinus Z score evolution was found between these groups. We did not find any differences concerning the occurrence of cardiovascular events between Marfan and Loeys–Dietz syndrome and their genetics subgroups. Aortic growth in men was significantly faster than in women (1.23 vs. 0.91 mm/year, P = 0.005). Marfan syndrome and Loeys–Dietz, as well as their genetics subgroups should be monitored similarly for the development of aortic root aneurysm. Like other phenotypic characteristics of these syndromes, the cardio vascular manifestations present a high variability among patients and a correlation genotype/phenotype is not informative for patient care. A possible exception is the TGFβ group, which may grow faster.

Impact of genotype on the progression of aortic disease in patients with Marfan syndrome and Loeys–Dietz syndrome

Marfan and Loeys–Dietz syndromes are connective tissue disorders characterized by high clinical variability. The major morbidity and mortality in both syndromes relate to the dilatation of the aorta predisposing to aortic tear. We investigated the putative relationship between the genotype, aortic growth speed and the occurrence of severe cardio vascular events (prophylactic surgery of the aortic root, aortic dissection or related death). We have performed a retrospective study of 102 patients with pathogenic variants in FBN1, TGFβR1 and R2 and SMAD3 genes followed at a Marfan reference center in France. The average age at the start of the study was 13.8 years and data were collected over 5 years. The FBN1 variants were classified as haploinsufficient (HI) or dominant negative (DN). Aortic diameters and aortic dilatation at the level of the Valsalva sinuses were assessed by echocardiography. No overall aortic growth difference was found between Marfan and Loeys–Dietz syndrome (1.14 vs. 1.11 mm/year, P = 0.74), neither between HI and DN groups (1.12 vs. 1.01 mm/year, P = 0.36). However, patients with a SMAD 3 mutation seem to have lower aortic growth than those in the TGFβ group (0.91 vs. 1.34 mm/year, P = 0.36). No difference concerning Valsalva sinus Z score evolution was found between these groups. We did not find any differences concerning the occurrence of cardio vascular events between Marfan and Loeys–Dietz syndrome and their genetics subgroups. Aortic growth in men was significantly faster than in women (1.23 vs. 0.91 mm/year, P = 0.005). Marfan syndrome and Loeys–Dietz, as well as their genetics subgroups should be monitored similarly for the development of aortic root aneurysm. Like other phenotypic characteristics of these syndromes, the cardio vascular manifestations present a high variability among patients and a correlation genotype/phenotype is not informative for patient care. A possible exception is the TGFβ group, which may grow faster.

Identification of novel genetic susceptibility loci for thoracic and abdominal aortic aneurysms via genome-wide association study using the UK Biobank Cohort.

Thoracic aortic aneurysm (TAA) and abdominal aortic aneurysm (AAA) are known to have a strong genetic component. In a genome-wide association study (GWAS) using the UK Biobank, we analyzed the genomes of 1,363 individuals with AAA compared to 27,260 age, ancestry, and sex-matched controls (1:20 case:control study design). A similar analysis was repeated for 435 individuals with TAA compared to 8,700 controls. Polymorphism with minor allele frequency (MAF) >0.5% were evaluated. We identified novel loci near LINC01021, ATOH8 and JAK2 genes that achieved genome-wide significance for AAA (p-value <5x10-8), in addition to three known loci. For TAA, three novel loci in CTNNA3, FRMD6 and MBP achieved genome-wide significance. There was no overlap in the genes associated with AAAs and TAAs. Additionally, we identified a linkage group of high-frequency variants (MAFs ~10%) encompassing FBN1, the causal gene for Marfan syndrome, which was associated with TAA. In FinnGen PheWeb, this FBN1 haplotype was associated with aortic dissection. Finally, we found that baseline bradycardia was associated with TAA, but not AAA. Our GWAS found that AAA and TAA were associated with distinct sets of genes, suggesting distinct underlying genetic architecture. We also found association between baseline bradycardia and TAA. These findings, including JAK2 association, offer plausible mechanistic and therapeutic insights. We also found a common FBN1 linkage group that is associated with TAA and aortic dissection in patients who do not have Marfan syndrome. These FBN1 variants suggest shared pathophysiology between Marfan disease and sporadic TAA.

Regulatory variants in TCF7L2 are associated with thoracic aortic aneurysm

Thoracic aortic aneurysm (TAA) is characterized by dilation of the aortic root or ascending/descending aorta. TAA is a heritable disease that can be potentially life threatening. While 10%-20% of TAA cases are caused by rare, pathogenic variants in single genes, the origin of the majority of TAA cases remains unknown. A previous study implicated common variants in FBN1 with TAA disease risk. Here, we report a genome-wide scan of 1,351 TAA-affected individuals and 18,295 control individuals from the Cardiovascular Health Improvement Project and Michigan Genomics Initiative at the University of Michigan. We identified a genome-wide significant association with TAA for variants within the third intron of TCF7L2 following replication with meta-analysis of four additional independent cohorts. Common variants in this locus are the strongest known genetic risk factor for type 2 diabetes. Although evidence indicates the presence of different causal variants for TAA and type 2 diabetes at this locus, we observed an opposite direction of effect. The genetic association for TAA colocalizes with an aortic eQTL of TCF7L2, suggesting a functional relationship. These analyses predict an association of higher expression of TCF7L2 with TAA disease risk. Invitro, we show that upregulation of TCF7L2 is associated with BCL2 repression promoting vascular smooth muscle cell apoptosis, a key driver of TAA disease.

Generation of two human induced pluripotent stem cell (hiPSC) lines derived from unrelated Marfan Syndrome patients

Marfan Syndrome (MFS) is a pleiotropic and autosomal dominant condition caused by pathogenic variants in FBN1. Although fully penetrant, clinical variability is frequently observed among patients and there are only few genotype-phenotype correlations described so far. Here, we describe the generation and characterization of hiPSC lines derived from two unrelated MFS patients harboring heterozygous variants in FBN1. Human iPSCs were obtained from erythroblasts reprogrammed with episomal vectors carrying the reprogramming factors OCT4, SOX2, KLF4, c-MYC and LIN-28, and characterized according to established criteria. Differentiated cells demonstrated different patterns of fibrillin-1 expression suggesting different molecular mechanisms between the two patients.

Generation of a human iPSC line QDMHi001-A from a patient with Marfan syndrome carrying a heterozygous c.6772 T > C variant in FBN1

Variants in FBN1 are associated with Marfan Syndrome, an autosomal dominant disorder with clinical features that involve the musculoskeletal, cardiovascular and ocular systems. We generated a human iPSC line QDMHi001-A from a patient with Marfan syndrome and a heterozygous c.6772 T > C (p.Cys2258Arg) variant in FBN1. This line will be a valuable resource for in vitro disease modeling and drug testing for Marfan syndrome.

An integrated clinical and molecular study of a cohort of Turkish patients with Marfan syndrome harboring known and novel FBN1 variants.

Marfan syndrome (MFS) is an autosomal dominant genetic condition that mainly affects connective tissue in many parts of the body. Cardinal manifestations involve the ocular, skeletal, and cardiovascular systems. The diagnosis of MFS relies on the revised Ghent criteria, outlined by international expert opinion to facilitate accurate recognition of this syndrome as well as to improve patient management and counseling. However, it may not always be possible to make a definitive diagnosis according to these criteria in each patient and thus molecular confirmation is necessary in subjects with suspected MFS. This debilitating, if not fatal, disorder is caused by mutations in FBN1, which encodes a major constitutive element of extracellular microfibrils. Here, we present a detailed clinical and molecular analysis of 76 Turkish patients with definitive or suspected MFS diagnosed at our center between 2014 and 2019. We were able to identify a total of 51 different FBN1 variants in our cohort, 31 of which have previously been reported in the relevant scientific literature. The remaining 20 variants have not been documented to date. In one patient, we detected a large deletion including the entire FBN1 gene using the array CGH approach. Currently, there are very few studies on the genotype-phenotype correlation of patients with MFS, and no clear genotype-phenotype maps for MFS have been constructed so far, except for some cases. We believe that our findings will make a rich and peculiar contribution to the elusive genotype-phenotype relationship in MFS, especially in this large and populous ethnic group.

Clinically relevant variants in a large cohort of Indian patients with Marfan syndrome and related disorders identified by next-generation sequencing

Marfan syndrome and related disorders are a group of heritable connective tissue disorders and share many clinical features that involve cardiovascular, skeletal, craniofacial, ocular, and cutaneous abnormalities. The majority of affected individuals have aortopathies associated with early mortality and morbidity. Implementation of targeted gene panel next-generation sequencing in these individuals is a powerful tool to obtain a genetic diagnosis. Here, we report on clinical and genetic spectrum of 53 families from India with a total of 83 patients who had a clinical diagnosis suggestive of Marfan syndrome or related disorders. We obtained a molecular diagnosis in 45/53 (85%) index patients, in which 36/53 (68%) had rare variants in FBN1 (Marfan syndrome; 63 patients in total), seven (13.3%) in TGFBR1/TGFBR2 (Loeys–Dietz syndrome; nine patients in total) and two patients (3.7%) in SKI (Shprintzen–Goldberg syndrome). 21 of 41 rare variants (51.2%) were novel. We did not detect a disease-associated variant in 8 (15%) index patients, and none of them met the Ghent Marfan diagnostic criteria. We found the homozygous FBN1 variant p.(Arg954His) in a boy with typical features of Marfan syndrome. Our study is the first reporting on the spectrum of variants in FBN1, TGFBR1, TGFBR2, and SKI in Indian individuals.

Parental mosaicism in Marfan and Ehlers\u2013Danlos syndromes and related disorders

Marfan syndrome (MFS) is a heritable connective tissue disorder (HCTD) caused by pathogenic variants in FBN1 that frequently occur de novo. Although individuals with somatogonadal mosaicisms have been reported with respect to MFS and other HCTD, the overall frequency of parental mosaicism in this pathology is unknown. In an attempt to estimate this frequency, we reviewed all the 333 patients with a disease-causing variant in FBN1. We then used direct sequencing, combined with High Resolution Melting Analysis, to detect mosaicism in their parents, complemented by NGS when a mosaicism was objectivized. We found that (1) the number of apparently de novo events is much higher than the classically admitted number (around 50% of patients and not 25% as expected for FBN1) and (2) around 5% of the FBN1 disease-causing variants were not actually de novo as anticipated, but inherited in a context of somatogonadal mosaicisms revealed in parents from three families. High Resolution Melting Analysis and NGS were more efficient at detecting and evaluating the level of mosaicism compared to direct Sanger sequencing. We also investigated individuals with a causal variant in another gene identified through our “aortic diseases genes” NGS panel and report, for the first time, on an individual with a somatogonadal mosaicism in COL5A1. Our study shows that parental mosaicism is not that rare in Marfan syndrome and should be investigated with appropriate methods given its implications in patient’s management.

A genotype-first approach to exploring Mendelian cardiovascular traits with clear external manifestations

PurposeThe purpose of this study is to use a genotype-first approach to explore highly penetrant, autosomal dominant cardiovascular diseases with external features, the RASopathies and Marfan syndrome (MFS), using biobank data. MethodsThis study uses exome sequencing and corresponding phenotypic data from Mount Sinai’s BioMe (n = 32,344) and the United Kingdom Biobank (UKBB; n = 49,960). Variant curation identified pathogenic/likely pathogenic (P/LP) variants in RASopathy genes and FBN1. ResultsTwenty-one subjects harbored P/LP RASopathy variants; three (14%) were diagnosed, and another 46% had ≥1 classic Noonan syndrome (NS) feature. Major NS features (short stature [9.5% p = 7e-5] and heart anomalies [19%, p < 1e-5]) were less frequent than expected. Prevalence of hypothyroidism/autoimmune disorders was enriched compared with biobank populations (p = 0.007). For subjects with FBN1 P/LP variants, 14/41 (34%) had a MFS diagnosis or highly suggestive features. Five of 15 participants (33%) with echocardiographic data had aortic dilation, fewer than expected (p = 8e-6). Ectopia lentis affected only 15% (p < 1e-5). ConclusionsSubstantial fractions of individuals harboring P/LP variants with partial or full phenotypic matches to a RASopathy or MFS remain undiagnosed, some not meeting diagnostic criteria. Routine population genotyping would enable multidisciplinary care and avoid life-threatening events.

Abstract 15966: Abnormal Left Ventricular Strain Correlates With Left Ventricular Dysfunction but Not Aortic Pathology in Marfan Syndrome in Children

Introduction: Cardiomyopathy has been described in some adults with Marfan syndrome (MFS), as demonstrated by low ejection fraction (EF) and abnormal left ventricular (LV) strain. Recent studies from our group show that LV dilation and decreased EF are common in children with MFS. However, LV strain remains understudied in children. Hypothesis: Abnormal strain is associated with lower EF, higher aortic root z-score and higher height-adjusted vertebral artery tortuosity index (VTI-h). In addition, abnormal strain with normal EF is associated with a subsequent decline in EF. Methods: Patients with MFS, defined as meeting Ghent 2010 criteria and a pathogenic FBN1 variant or ectopia lentis, &lt;19 years of age at first cardiac magnetic resonance imaging study (CMR) from 2003-2018 were included. CMR LV circumferential and longitudinal strain were measured using feature tracking software. CMR aortic root Z-scores were calculated using both pediatric echocardiographic formulas and MRI reference data. VTI-h was measured using previously described methods. We evaluated initial CMR for associations between strain, EF, root z-scores, and VTI using Spearman correlation. A secondary analysis was performed limiting to patients with a normal EF on initial CMR, evaluating for associations between initial strain values and the outcomes of sustained normal EF versus development of low EF (&lt;55%). Results: Of 31 included patients, median age at first CMR was 13.5 y (IQR 10.7-16.2 y). Worse circumferential strain was associated with lower EF (basal: rho = -0.586, p = 0.001; mid: rho = -0.573, p = 0.001; apical: rho = -0.406, p = 0.026), while longitudinal strain was not associated with EF (p = 0.063, 0.257, 0.260). Neither circumferential nor longitudinal strain were associated with aortic root z-score or VTI-h. Among patients with normal EF, initial circumferential strain was not different between patients who maintained normal EF or developed low EF. Conclusions: Worse LV circumferential strain was associated with lower EF in children with MFS, while longitudinal strain was not. Abnormal strain was not associated with aortic pathology or later development of reduced EF. This suggests that the cardiomyopathy seen in children with MFS is likely independent of aortic pathology.

A nonsense variant in FBN1 caused autosomal dominant Marfan syndrome in a Chinese family: a case report

BackgroundMarfan syndrome (MFS) is a common autosomal dominant inherited disease, and the occurrence rate is around 0.1–0.2‰. The causative variant of FNB1 gene accounts for approximately 70–80% of all MFS cases. In this study, we found a heterozygous c.3217G > T (p.Glu1073*) nonsense variant in the FBN1 gene. This finding extended the variant spectrum of the FBN1 gene and will provide a solution for patients to bear healthy offspring by preimplantation genetic testing or prenatal diagnosis.Case presentationThe patient was treated due to tachycardia during excitement in a hospital. Echocardiography showed dilatation of the ascending aorta and main pulmonary artery, mitral regurgitation (mild), tricuspid regurgitation (mild), and abnormal left ventricular filling. Electrocardiograph showed sinus rhythm. In addition, flutters of shadows in front of his eyes and vitreous opacity were present in the patient. Genomic DNA was extracted from peripheral blood samples from members of the family and 100 unrelated controls. Potential variants were screened out by next-generation sequencing and confirmed by MLPA & Sanger sequencing. Real-time fluorescence quantitative PCR (RT-qPCR) was performed to detect the relative mRNA quantitation in the patient. A heterozygous nonsense variant c.3217G > T of the FBN1 gene, which resulted in p. Glu1073Term, was identified in both patients. Only wild type bases were found in the cDNA sequence of the patient. Real-time fluorogenic quantitative PCR results showed that the relative expression level of FBN1 cDNA in the patient was only about 21% compared to that of normal individuals. This variant c.3217G > T of the FBN1 gene introduces a Stop codon in the cb-EGF12 domain. We speculated that a premature translational-termination codon (PTC) was located in the mRNA and the target mRNA was disintegrated through a process known as nonsense-mediated mRNA decay (NMD), which led to a significant decrease of the fibrillin-1 protein, eventually causing clinical symptoms in the patient.ConclusionsIn this study, we found a heterozygous c.3217G > T (p.Glu1073*) nonsense variant in the FBN1 gene, which eventually led to Marfan syndrome in a Chinese family.

Genotype-Phenotype Correlation in Children: The Impact of FBN1 Variants on Pediatric Marfan Care.

Currently, no reliable genotype–phenotype correlation is available for pediatric Marfan patients in everyday clinical practice. We investigated correlations of FBN1 variants with the prevalence and age of onset of Marfan manifestations in childhood and differentiated three groups: missense/in-frame, splice, and nonsense/frameshift variants. In addition, we differentiated missense variants destroying or generating a cysteine (cys-missense) and alterations not affecting cysteine. We categorized 105 FBN1-positive pediatric patients. Patients with cys-missense more frequently developed aortic dilatation (p = 0.03) requiring medication (p = 0.003), tricuspid valve prolapse (p = 0.03), and earlier onset of myopia (p = 0.02) than those with other missense variants. Missense variants correlated with a higher prevalence of ectopia lentis (p = 0.002) and earlier onset of pulmonary artery dilatation (p = 0.03) than nonsense/frameshift, and dural ectasia was more common in the latter (p = 0.005). Pectus excavatum (p = 0.007) appeared more often in patients with splice compared with missense/in-frame variants, while hernia (p = 0.04) appeared earlier in the latter. Findings on genotype–phenotype correlations in Marfan-affected children can improve interdisciplinary therapy. In patients with cys-missense variants, early medical treatment of aortic dilatation seems reasonable and early regular ophthalmologic follow-up essential. Patients with nonsense/frameshift and splice variants require early involvement of orthopedic specialists to support the growing child.

Double heterozygous variants in FBN1 and FBN2 in a Thai woman with Marfan and Beals syndromes

A phenotype of an individual is resulted from an interaction among variants in several genes. Advanced molecular technologies allow us to identify more patients with mutations in more than one genes. Here, we studied a Thai woman with combined clinical features of Marfan (MFS) and Beals (BS) syndromes including frontal bossing, enophthalmos, myopia, the crumpled appearance to the top of the pinnae, midface hypoplasia, high arched palate, dermal stretch marks, aortic enlargement, mitral valve prolapse and regurgitation, aortic root dilatation, and progressive scoliosis. The aortic root enlargement was progressive to a diameter of 7.2 cm requiring an aortic root replacement at the age of 8 years. At her last visit when she was 19 years old, she had moderate aortic regurgitation. Exome sequencing revealed that she carried the c.3159C > G (p.Cys1053Trp) in exon 26 of FBN1 and c.2638G > A (p. Gly880Ser) in exon 20 of FBN2. The variant in FBN1 was de novo, while that in FBN2 was inherited from her unaffected mother. Both genes encode for fibrillins, which are essential for elastic fibers and can form the heterotypic microfibrils. Two defective fibrillins may synergistically worsen cardiovascular manifestations seen in our patient. In this study, we identified the fourth patient with both MFS and BS, carrying mutations in both FBN1 and FBN2.