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

Introduction: Cardiomyopathies are diseases of the heart muscle and are important causes of heart failure. Dilated cardiomyopathy (DCM) is a common form of cardiomyopathy that can be acquired, syndromic or non-syndromic. The current study was conducted to explore the genetic defects in a Pakistani family with cardiac disease and features of Marfan’s syndrome (MFS). Methods: A family with left ventricle (LV) diastolic dysfunction and MFS phenotype was assessed in Pakistan. The clinical information and blood samples from the patients were collected after physical, cardiovascular, and ophthalmologic examinations. An affected individual (proband) was subjected to whole-exome sequencing (WES). The findings were further validated through Sanger sequencing in the family. Results: Through WES and sanger validation, we identified a novel variant NM_000138.4; c.1402A>G in the Fibrillin-1 (FBN1) gene that segregates with LV diastolic dysfunction and MFS. Furthermore, bioinformatic evaluation suggested that the novel variant is deleterious and disease-causing. Conclusions: This study identified for the first time a novel FBN1 variant in a family with LV diastolic dysfunction and MFS in Pakistan.

Marfan Syndrome Caused by Disruption of the FBN1 Gene due to A Reciprocal Chromosome Translocation

Marfan syndrome (MFS) is a hereditary connective tissue disease caused by heterozygous mutations in the fibrillin-1 gene (FBN1) located on chromosome 15q21.1. A complex chromosomal rearrangement leading to MFS has only been reported in one case so far. We report on a mother and daughter with marfanoid habitus and no pathogenic variant in the FBN1 gene after next generation sequencing (NGS) analysis, both showing a cytogenetically reciprocal balanced translocation between chromosomes 2 and 15. By means of fluorescence in situ hybridization of Bacterial artificial chromosome (BAC) clones from the breakpoint area on chromosome 15 the breakpoint was narrowed down to a region of approximately 110 kb in FBN1. With the help of optical genome mapping (OGM), the translocation breakpoints were further refined on chromosomes 2 and 15. Sequencing of the regions affected by the translocation identified the breakpoint of chromosome 2 as well as the breakpoint of chromosome 15 in the FBN1 gene leading to its disruption. To our knowledge, this is the first report of patients with typical clinical features of MFS showing a cytogenetically reciprocal translocation involving the FBN1 gene. Our case highlights the importance of structural genome variants as an underlying cause of monogenic diseases and the useful clinical application of OGM in the elucidation of structural variants.

Clinical and genetic characteristics of rare variants of acromelic skeletal dysplasias caused by mutations in the FBN1 gene

BACKGROUND: Geleophysic dysplasia and acromicric dysplasia are rare hereditary diseases characterized by dwarfism and dysplastic skeletal features. In the literature, only a few cases of geleophysic dysplasia and acromicric dysplasia caused by mutations in the FBN1 gene are described. CLINICAL CASES: A description of the clinical and genetic characteristics of three female patients with acromelic dysplasias caused by three types of missense mutations in the FBN1 gene is presented. In two patients, on the basis of clinical manifestations and radiographic examination, acromicric dysplasia, and in one patient geleophysic dysplasia were diagnosed. It was shown that all identified mutations were localized in exons of the FBN1 gene encoding the amino acid sequence of the fifth domain, which has homology with transforming growth factor-beta. DISCUSSION: We have analyzed the clinical and genetic correlations to confirm the previously stated hypothesis about the occurrence of a severe phenotype of geleophysic dysplasia in patients with the c.5206T C mutation. This mutation is characterized by the replacement of cysteine by arginine in the position of the polypeptide chain leading to moderate clinical manifestations of acromicric dysplasia in patients with the c.5284 G A (p. Gly1762Ser). It was shown that the previously undescribed substitution c.5177G A (p.Gly1726Asp and another previously described mutation in this codon resulted in the replacement of glutamine with valine. This mutation causes the appearance of a less pronounced phenotype of AD. CONCLUSIONS: Based on the results of the examination of three Russian patients and analysis of clinical and radiographic parameters described in the literature, we reported that mutations in the FBN1 gene disrupted the amino acid sequence of the fifth like transforming growth factor-beta domain of fibrillin type 1. Importantly, these mutations are responsible for the occurrence of geleophysic dysplasia and acromicric dysplasia. However, the most severe clinical manifestations were observed in patients with mutations leading to the substitution of cysteine for arginine at the position of the polypeptide chain 1736. This may lead to affecting the transforming growth factor-beta signaling pathway.

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

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. FUNDunding Acknowledgement Type of funding sources: None. Figure 1

Marfan syndrome: genetic variant determinants of cardiovascular outcomes

Background Marfan syndrome is a systemic connective tissue disorder caused by genetic variants in the fibrillin-1 (FBN1) gene. Cardiovascular complications are the leading cause of mortality. Purpose To compare cardiovascular outcome by gender and by type of the genetic variant in the FBN1 gene. Materials and methods We analyzed clinical data on 1956 carriers and affected relatives with 1430 pathogenic or likely pathogenic genetic variants in the FBN1 gene (including cases identified in our laboratory and cases described in the literature) in whom age at last follow-up was available. We excluded patients with pathogenic or likely pathogenic genetic variants located in the so-called “neonatal region” (exon 24–32); they are recognized to have an early onset/severe phenotype. Kaplan-Meier survival curves were generated to examine gender and type of genetic variant in relation to survival free of surgical intervention or cardiovascular (CV) death (composite of deaths related to aortic dissection, heart failure/transplant, sudden, stroke or CV surgery). Genetic variants were classified as truncating (nonsense, frameshift and splicing), “missense non-neonatal” and only those missense eliminating a Cysteine residue in the non-neonatal region (“Cys non-neonatal”). Results Data were examined on 896 patients with truncating variants (53% male; 47% female) and 1060 with missense variants, located outside the “neonatal region” (54% male; 46% female). Of these, 475 were missense variants substituting a cysteine residue (52% male; 48% female). Those with truncating variants had worse prognosis versus those with missense and Cys variants (p=0.000108 and p=0.000115), with earlier onset of cardiovascular events. Overall, patients with missense variants had similar prognosis to those with missense variants eliminating a Cysteine residue. By age 65, however, almost 50% of patients with any type of variant had suffered a CV event, and with each variant type males had worse prognosis (see Figure 1). This was most evident in males aged 30 to 50 with missense variants that substituted a Cysteine residue, while female carriers of these variants had a prognosis similar to other missense variants (see Figure 2). During the first decade carriers of missense and truncating variants mainly died of heart failure. From age 10 to 50, aortic dissection was the most common event, while later other events became more frequent, e.g. vascular intervention and sudden death. Conclusion In our cohort, male carriers of pathogenic or likely pathogenic variants had worse prognosis versus females. Carriers of truncating variants had the worst CV outcomes. However, it is noteworthy that by age 65, regardless of gender or mutation type, close to 50% of patients had experienced a major CV event/death. FUNDunding Acknowledgement Type of funding sources: Private company. Main funding source(s): Health in Code Figure 2. Type by gender

Narrowing of the neonatal region in the FBN1 gene

Background Neonatal Marfan syndrome (MFS) is considered the most severe form of MFS and is characterized by early childhood death due to congestive heart failure. It has been suggested that genetic variants associated with this clinical presentation, cluster in a specific region between exons 24 and 32. It has been reported that patients carrying genetic variants in these exons have worse prognosis. Purpose Our purpose was to analyze cardiovascular outcome by location of the genetic variants in the “neonatal region” of the FBN1 gene. Materials and methods We analyzed clinical data on 1353 carriers and affected relatives with 683 missense pathogenic or likely pathogenic genetic variants of FBN1 gene (including cases identified in our laboratory and cases described in the literature) in whom age at last follow-up was available. Kaplan-Meier survival curves were generated to examine location of the genetic variant in the FBN1 gene in relation to survival free of surgical intervention or cardiovascular (CV) death (composite of deaths related to aortic dissection, heart failure/transplant, sudden, stroke or CV surgery). Missense genetic variants were classified as located in the “neonatal region” (residues 952–1363, corresponding to exons 24–32) and in the “non-neonatal region” (residues 45–951 and 1364–2731). In the “neonatal region”, we have also analyzed a sub-region of “over-representation” of heart failure deaths in the first year of life, which we called “critical neonatal region” (amino acids 1028–1088, corresponding to exon 25 and few residues from exon 26) in comparison to the “non-critical neonatal region”. Results Data were examined on 1060 patients with missense variants located in the “non neonatal region” and on 293 patients with missense variants located in the “neonatal region”. Of these, 96 patients were carriers of missense variants in the “critical neonatal region”, the rest of patients carried variants in the neonatal region, outside this particular domain (“non-critical neonatal region”). Patients carrying missense variants in the neonatal region had worse prognosis than those carrying variants outside this region. This poorer outcome was due to events occurring in patients carrying variants in the “critical neonatal region” (see Figure). These patients had the worse prognosis (p=0.000108, vs. the other groups). Furthermore, events in the non-critical neonatal region were similar to other missense variants located outside the neonatal region. There were no differences in the “neonatal region” when analyzing by gender. Conclusion In our cohort, the worse prognosis seen in patients carrying missense pathogenic or likely pathogenic variants in the “neonatal region” compared to the “non-neonatal region”, was due to events in patients carrying missense variants in a small subregion which we called the “critical-neonatal region” (exons 25 and 26). These patients had the worse prognosis, irrespective of gender. FUNDunding Acknowledgement Type of funding sources: Private company. Main funding source(s): Health in Code Figure 1. Neonatal region FBN1

Family history of aortic dissection is not a risk factor in Marfan syndrome with a FBN1 gene mutation

Background A history family of aortic dissection was considered as a risk factor for aortic dissection in patients with Marfan syndrome with a FBN1 mutation. Objectives Evaluate whether a family history of aortic dissection is a risk marker for dissection in this population Methods Retrospective study of patients coming to the reference centre between 1996 and 2018, carrying a FBN1 gene mutation. Pedigrees were obtained for each patient, and familial screening actively pursued. Patients with a family history of aortic dissection were compared with patients without family history of aortic dissection. Results 1700 patients (age 33.2 (±17) years, 51% women) with a FBN1 gene mutation were included. 145 (8,5%) patients underwent aortic dissection at a mean age of 37.9 (±11.4) years and 323 (19%) patients had been operated at 33.8 (±13.9) years. 481 patients had a family history of aortic dissection, including 38 who dissected themselves, and 88 who underwent surgery. 1219 had no family history of aortic dissection, including 107 who dissected themselves, and 235 who underwent surgery. Therefore, the personal risk for aortic dissection was similar in patients with and without a family history of aortic dissection (38/481, i.e. 7.9% vs 107/1219, i.e. 8.8%), as was the personal risk for prophylactic aortic surgery (88/481, i.e. 18.3% vs. 253/1219, i.e. 17.2%), and the risk for either aortic dissection or prophylactic aortic surgery (118/481, i.e. 24.5% vs. 328/1219, i.e. 26.9%). Conclusions In Marfan syndrome with a FBN1 gene mutation, a family history of aortic dissection is not a marker of aortic disease severity. FUNDunding Acknowledgement Type of funding sources: None.