Novel FBN1 mutations are responsible for cardiovascular manifestations of Marfan syndrome

Association between pectus excavatum and congenital genetic disorders: A systematic review and practical guide for the treating physician

BACKGROUND

Pectus excavatum (PE) could be part of a genetic disorder, which then has implications regarding comorbidity, the surgical correction of PE, and reproductive choices. However, referral of a patient presenting with PE for genetic analysis is often delayed because additional crucial clinical signs may be subtle or even missed in syndromic patients. We reviewed the literature to inventory known genetic disorders associated with PE and create a standardized protocol for clinical evaluation.

METHODS

A systematic literature search was performed in electronic databases. Genetic disorders were considered associated with PE if studies reported at least five cases with PE. Characteristics of each genetic disorder were extracted from the literature and the OMIM database in order to create a practical guide for the clinician.

RESULTS

After removal of duplicates from the initial search, 1632 citations remained. Eventually, we included 119 full text articles, representing 20 different genetic disorders. Relevant characteristics and important clinical signs of each genetic disorder were summarized providing a standardized protocol in the form of a scoring list. The most important clinical sign was a positive family history for PE and/or congenital heart defect.

CONCLUSIONS

Twenty unique genetic disorders have been found associated with PE. We have created a scoring list for the clinician that systematically evaluates crucial clinical signs, thereby facilitating decision making for referral to a clinical geneticist.

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.

CRISPR/Cas9 in zebrafish: An attractive model for FBN1 genetic defects in humans

Background

Mutations in the fibrillin‐1 gene (FBN1) are associated with various heritable connective tissue disorders (HCTD). The most studied HCTD is Marfan syndrome. Ninety percent of Marfan syndrome is caused by mutations in the FBN1 gene. The zebrafish share high genetic similarity to humans, representing an ideal model for genetic research of human diseases. This study aimed to generate and characterize fbn1^+/− mutant zebrafish using the CRISPR/Cas9 gene‐editing technology.

Methods

CRISPR/Cas9 was applied to generate an fbn1 frameshift mutation (fbn1^+/−) in zebrafish. F1 fbn1^+/− heterozygotes were crossed with transgenic fluorescent zebrafish to obtain F2 fbn1^+/− zebrafish. Morphological abnormalities were assessed in F2 fbn1^+/− zebrafish by comparing with the Tuebingen (TU) wild‐type controls at different development stages.

Results

We successfully generated a transgenic line of fbn1^+/− zebrafish. Compared with TU wild‐type zebrafish, F2 fbn1^+/− zebrafish exhibited noticeably decreased pigmentation, increased lengths, slender body shape, and abnormal cardiac blood flow from atrium to ventricle.

Conclusion

We generated the first fbn1^+/− zebrafish model using CRISPR/Cas9 gene‐editing approach to mimic FBN1 genetic defects in humans, providing an attractive model of Marfan syndrome and a method to determine the pathogenicity of gene mutation sites.

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.

Identification of Novel Causal FBN1 Mutations in Pedigrees of Marfan Syndrome

Marfan syndrome (MFS) is an autosomal dominant genetic disorder of the connective tissue, typically characteristic of cardiovascular manifestations, valve prolapse, left ventricle enlargement, and cardiac failure. Fibrillin-1 (FBN1) is the causative gene in the pathogenesis of MFS. Patients with different FBN1 mutations often present more considerable phenotypic variation. In the present study, three affected MFS pedigrees were collected for genetic analysis. Using next-generation sequencing (NGS) technologies, 3 novel frameshift pathogenic mutations which are cosegregated with affected subjects in 3 pedigrees were identified. These novel mutations provide important diagnostic and therapeutic insights for precision medicine in MFS, especially regarding the lethal cardiovascular events.