Three novel mutations of the fibrillin-1 gene and ten single nucleotide polymorphisms of the fibrillin-3 gene in Marfan syndrome patients

Application of Whole Exome Sequencing and Functional Annotations to Identify Genetic Variants Associated with Marfan Syndrome

Marfan syndrome (MFS) is a rare disease that affects connective tissue, which causes abnormalities in several organ systems including the heart, eyes, bones, and joints. The autosomal dominant disorder was found to be strongly associated with FBN1, TGFBR1, and TGFBR2 mutations. Although multiple genetic mutations have been reported, data from Asian populations are still limited. As a result, we utilized the whole exome sequencing (WES) technique to identify potential pathogenic variants of MFS in a Taiwan cohort. In addition, a variety of annotation databases were applied to identify the biological functions as well as the potential mechanisms of candidate genes. In this study, we confirmed the pathogenicity of FBN1 to MFS. Our results indicated that TTN and POMT1 may be likely related to MFS phenotypes. Furthermore, we found nine unique variants highly shared in a MFS family cohort, of which eight are novel variants worthy of further investigation.

Genotype variant screening and phenotypic analysis of FBN1 in Chinese patients with isolated ectopia lentis

Isolated ectopia lentis (IEL) can lead to blindness as result of severe complications, such as retinal detachment and secondary glaucoma. Pathogenic variants in the fibrillin 1 (FBN1) gene are a common cause of IEL. The aim of the present study was to investigate the frequency of pathogenic FBN1 variants in twelve probands with IEL and to evaluate their associated phenotypes. Systemic clinical examination of the twelve probands indicated that all had bilateral EL with a median age at diagnosis of three years. High myopia was the most common feature among the probands (83.3%; 10/12 cases). No extraocular symptoms (either cardiovascular or skeletal) were observed among these patients. Genomic DNA was extracted from peripheral blood leukocytes from all patients for targeted exome sequencing. Seven heterozygous missense variants in FBN1 were identified by bioinformatics analysis and further verified using Sanger sequencing. The seven variants were all classified as pathogenic after segregation analysis on available family members according to the American College of Medical Genetics and Genomics standards and guidelines. Of the seven variants, three were novel, namely c.2179T>C, c.2496T>G and c.3346G>C. The remaining four, namely c.184C>T, c.367T>C, c.1879C>T and c.4096G>A have been reported in previous studies. The seven pathogenic variants were identified in 8/12 (66.7%) probands with IEL. These results expand the variant spectrum of the FBN1 gene as well as the understanding of the molecular pathogenesis of IEL.

The Molecular Genetics of Marfan Syndrome

Marfan syndrome (MFS) is a complex connective tissue disease that is primarily characterized by cardiovascular, ocular and skeletal systems disorders. Despite its rarity, MFS severely impacts the quality of life of the patients. It has been shown that molecular genetic factors serve critical roles in the pathogenesis of MFS. FBN1 is associated with MFS and the other genes such as FBN2, transforming growth factor beta (TGF-β) receptors (TGFBR1 and TGFBR2), latent TGF-β-binding protein 2 (LTBP2) and SKI, amongst others also have their associated syndromes, however high overlap may exist between these syndromes and MFS. Abnormalities in the TGF-β signaling pathway also contribute to the development of aneurysms in patients with MFS, although the detailed molecular mechanism remains unclear. Mutant FBN1 protein may cause unstableness in elastic structures, thereby perturbing the TGF-β signaling pathway, which regulates several processes in cells. Additionally, DNA methylation of FBN1 and histone acetylation in an MFS mouse model demonstrated that epigenetic factors play a regulatory role in MFS. The purpose of the present review is to provide an up-to-date understanding of MFS-related genes and relevant assessment technologies, with the aim of laying a foundation for the early diagnosis, consultation and treatment of MFS.

Identification of Novel Clinically Relevant Variants in 70 Southern Chinese patients with Thoracic Aortic Aneurysm and Dissection by Next-generation Sequencing

Thoracic Aortic Aneurysm and Dissection (TAAD) is a life-threatening pathology and remains challenging worldwide. Up to 40% of TAAD are hereditary with complex heterogeneous genetic backgrounds. Recently, next-generation sequencing (NGS) has been successfully applied to identify genetic variants in an efficient and cost-effective manner. In our study, NGS coupled with DNA target-capture array was used to screen 11 known causative genes of TAAD in 70 patients from Southern China. All the identified variants were confirmed by Sanger sequencing. We identified forty variants in 36 patients (51.4%), including three known pathogenic (7.5%), 10 likely pathogenic variants (25%, 9 in FBN1, 1 in ACTA2), and 27 variants with uncertain significance (VUS) (67.5%). Among the 27 VUS, 14 (51.9%) were in the FBN1 gene, 3 in Col5A2, 2 in ACTA2, 2 in MYH11, 2 in MYLK, 2 in SLC2A10, 1 in MSTN and 1 in SMAD3 respectively. Based on the segregation data and independent reports, five known likely pathogenic variants and four VUS were upgraded to pathogenic variant and likely pathogenic variant respectively. Our data indicate that NGS is a highly efficient genetic method for identification of pathogenic variants in TAAD patients.

Identification of 29 novel and nine recurrent fibrillin-1 (FBN1) mutations and genotype-phenotype correlations in 76 patients with Marfan syndrome

Marfan syndrome (MFS) is an autosomal-dominant disorder of the fibrous connective tissue that is typically caused by mutations in the gene coding for fibrillin-1 (FBN1), a major component of extracellular microfibrils. The clinical spectrum of MFS is highly variable and includes involvement of the cardiovascular, skeletal, ocular, and other organ systems; however, the genotype-phenotype correlations have not been well developed. Various screening methods have led to the identification of about 600 different mutations (FBN1-UMD database; www.umd.be). In this study we performed SSCP and/or direct sequencing to analyze all 65 exons of the FBN1 gene in 116 patients presenting with classic MFS or related phenotypes. Twenty-nine novel and nine recurrent mutations were identified in 38 of the analyzed patients. The mutations comprised 18 missense (47%), eight nonsense (21%), and five splice site (13%) mutations. Seven further mutations (18%) resulted from deletion, insertion, or duplication events, six of which led to a frameshift and subsequent premature termination. Additionally, we describe new polymorphisms and sequence variants. On the basis of the data presented here and in a previous study, we were able to establish highly significant correlations between the FBN1 mutation type and the MFS phenotype in a group of 76 mutation-positive patients for whom comprehensive clinical data were available. Most strikingly, there was a significantly lower incidence of ectopia lentis in patients who carried a mutation that led to a premature termination codon (PTC) or a missense mutation without cysteine involvement in FBN1, as compared to patients whose mutations involved a cysteine substitution or splice site alteration.