AFBN1 gene in patients with Marfan syndrome

30 exons have been analyzed using SSCP in patients with MFS or related phenotypes. We report 2 missense mutations occur in calcium-binding Epidermal Growth Factor-like (EGFcb) domains and 9 polymorphisms located both in coding and noncoding regions of FBN1 gene. Three intragenic microsatellite polymorphic markers MTS-1, MTS-2 and MTS-4 have been analyzed in patients with MFS and unrelated unaffected control individuals. We found significant differences in allele frequency distribution of MTS-2 and MTS-4 loci between MFS patients and unaffected individuals. Haplotype frequency distribution on normal and mutant chromosomes were significantly different. The most common haplotype was 2-11-8 which was predominant on normal chromosomes of affected individuals. Haplotype 2-2-8 was observed in 18% of cases on mutant chromosomes and in 4% of cases on normal chromosomes. These data demonstrate possibility and application of haplotype-segregation analysis with use of these intragenic markers for diagnostic purposes in affected families by Marfan's syndrome.     

Marfan syndrome: whole-exome sequencing reveals de novo mutations,second gene and genotype–phenotype correlations in the Chinese population

Marfan syndrome (MFS) is a dominant monogenic disease caused by mutations in fibrillin 1 (FBN1). Cardiovascular complications are the leading causes of mortality among MFS. In the present study, a whole-exome sequencing of MFS in the Chinese population was conducted to investigate the correlation between FBNI gene mutation and MFS. Forty-four low-frequency harmful loci were identified for the FBN1 gene in HGMD database. In addition, 38 loci were identified in the same database that have not been related to MFS before. A strict filtering and screening protocol revealed two patients of the studied group have double mutations in the FBN1 gene. The two patients harboring the double mutations expressed a prominent, highly pathological phenotype in the affected family. In addition to the FBN1 gene, we also found that 27 patients had mutations in the PKD1 gene, however these patients did not have kidney disease, and 16 of the 27 patients expressed aortic related complications. Genotype-phenotype analysis showed that patients with aortic complications are older in the family, aged between 20 and 40 years.     

Novel <Emphasis Type="Italic">FBN1</Emphasis> mutations are responsible for cardiovascular manifestations of Marfan syndrome

The fibrillin-1 (FBN1) gene mutations result in Marfan syndrome (MFS) and have a variety of phenotypic variations. This disease is involved in the skeletal, ocular and cardiovascular system. Here we analyzed genotype-phenotype correlation in two Chinese families with MFS. Two patients with thoracic aortic aneurysms and dissections were diagnosed as MFS according to the revised Ghent criteria. Peripheral blood samples were collected and genomic DNAs were isolated from available cases, namely, patient-1 and his daughter and son, and patient-2 and his parents. According to the next-generation sequencing results, the mutations in FBN1 were confirmed by direct sequencing. A heterozygous frameshift mutation in exon 12 of FBN1 was found in the proband-1 and his daughter. They showed cardiovascular phenotype thoracic aortic aneurysms and dissections, a life-threatening vascular disease, and atrial septal defect respectively. One de novo missense mutation in exon 50 of FBN1 was identified only in the patient-2, showing aortic root aneurysm and aortic root dilatation. Intriguingly, two novel mutations mainly caused the cardiovascular complications in affected family members. No meaningful mutations were found in these two patients by screening all exons of 428 genes related with cardiovascular disease. The high incidence of cardiovascular manifestations might be associated with the two novel mutations in exon 12 and 50 of FBN1.     

Relation between genotype and left-ventricular dilatation in patients with Marfan syndrome

Cardiovascular manifestations in patients with Marfan syndrome (MFS) are related to aortic and valvular abnormalities. However, dilatation of the left ventricle (LV) can occur, even in the absence of aortic surgery or valvular abnormalities. We evaluated genetic characteristics of patients with MFS with LV dilatation. One hundred eighty-two patients fulfilling the MFS criteria, without valvular abnormalities or previous aortic surgery, with a complete FBN1 analysis, were studied. FBN1 mutations were identified in over 81% of patients. Twenty-nine patients (16%) demonstrated LV dilatation (LV end diastolic diameter corrected for age and body surface area > 112%). FBN1-positive patients carrying a non-missense mutation more often had LV dilatation than missense mutation carriers (14/74 versus 5/75; p < 0.05). Finally, FBN1-negative MFS patients significantly more often demonstrated LV dilatation than FBN1-positive patients (10/33 versus 19/149; p < 0.05). It is concluded that LV dilatation in MFS patients is more often seen in patients with a non-missense mutation and in those patients without an FBN1 mutation. Therefore physicians should be aware of the possibility of LV dilatation in these patients even in the absence of valvular pathology.     

Association between Fibrillin1 Polymorphisms (rs2118181, rs10519177) and Transforming Growth Factor β1 Concentration in Human Plasma

Transforming growth factor (TGF)-β1 is a cytokine that participates in a broad range of cellular regulatory processes and is associated with various diseases including aortic aneurysm. Increased TGF-β1 levels are linked to Marfan syndrome (MFS) caused by fibrillin1 (FBN1) mutations and subsequent defects in signaling system. FBN1 single nucleotide polymorphisms (SNPs) rs2118181 and rs1059177 do not cause MFS but are associated with dilative pathology of aortic aneurysms (DPAAs). TGF-β1 and FBN1 SNPs rs2118181 and rs1059177 are potential biomarkers for early diagnosis of DPAA. We investigated the relationship between TGF-β1 levels in human blood plasma and FBN1 rs2118181 and rs1059177 in 269 individuals. The results showed a quantitative dependence of SNP genotype and TGF-β1 concentration. Presence of a single rs2118181 minor allele (G) increased the amount of TGF-β1 by roughly 1 ng/mL. Two copies of FBN1 rs1059177 minor allele (G) were required to have an additive effect on TGF-β1 levels. We found higher TGF-β1 concentrations in men compared with women (p = 0.001). A strong correlation between TGF-β1 levels and FBN1 SNPs suggests that a single nucleotide substitution in FBN1 sequence might reduce bioavailability or binding properties of fibrillin-1 and have an effect on TGF-β1 activation and cytokine concentration in blood plasma. By establishing the relationship between TGF-β1 and FBN1 SNPs rs2118181 and rs1059177, we provide evidence that their combination might be used as molecular biomarkers to identify patients at risk for sporadic ascending aortic aneurysm and aortic dissection.     

Evaluation of clinical significance of с.2956G&gt;A (rs112287730) polymorphism in <Emphasis Type="Italic">FBN1</Emphasis> gene in Marfan syndrome

Marfan syndrome (MFS) is an autosomal dominant inherited systemic disorder of connective tissue with many clinical manifestations in the cardiovascular, skeletal, and ocular systems. MFS is caused by mutations in the fibrillin-1 (FBN1) gene. To date, about 2000 FBN1 pathogenic variants that cause MFS or related phenotypes have been described. The c.2956G>A, p.Ala986Thr substitution (exon 25) in the FBN1 gene is described in the SNP database as rs112287730 with allele frequency of 0.02%. Although numerous published data exist, the clinical significance of this variant is unknown. Some studies identify this substitution as probably a pathogenic mutation, and others, as a polymorphism. Among Russian Marfan patients, the heterozygous c.2956G>A substitution was identified in four probands; three of them had familial history. To determine the clinical significance of this substitution, a segregation analysis of DNA samples of affected and unaffected family members was conducted. In the first case, a segregation of the c.2956G>A substitution with the disease was observed in the family: this substitution was detected in the heterozygous state in the three affected members, but not in the one unaffected member. However, the opposite observation occurred in the second familial case: three affected members did not have the c.2956G>A substitution, whereas it was found in one unaffected member. In addition, the molecular-genetic analysis of 110 ethnically unrelated unexplored individuals was performed. The c.2956G>A substitution was identified in two of 220 examined chromosomes (allele frequency 0.9%). Thus, it was established that the c.2956G>A substitution appears to be a polymorphism (nonpathogenic variant) and cannot cause MFS.     

Fibrillin 5 Is Essential for Plastoquinone-9 Biosynthesis by Binding to Solanesyl Diphosphate Synthases in Arabidopsis

Fibrillins are lipid-associated proteins in plastids and are ubiquitous in plants. They accumulate in chromoplasts and sequester carotenoids during the development of flowers and fruits. However, little is known about the functions of fibrillins in leaf tissues. Here, we identified fibrillin 5 (FBN5), which is essential for plastoquinone-9 (PQ-9) biosynthesis in Arabidopsis thaliana. Homozygous fbn5-1 mutations were seedling-lethal, and XVE:FBN5-B transgenic plants expressing low levels of FBN5-B had a slower growth rate and were smaller than wild-type plants. In chloroplasts, FBN5-B specifically interacted with solanesyl diphosphate synthases (SPSs) 1 and 2, which biosynthesize the solanesyl moiety of PQ-9. Plants containing defective FBN5-B accumulated less PQ-9 and its cyclized product, plastochromanol-8, but the levels of tocopherols were not affected. The reduced PQ-9 content of XVE:FBN5-B transgenic plants was consistent with their lower photosynthetic performance and higher levels of hydrogen peroxide under cold stress. These results indicate that FBN5-B is required for PQ-9 biosynthesis through its interaction with SPS. Our study adds FBN5 as a structural component involved in the biosynthesis of PQ-9. FBN5 binding to the hydrophobic solanesyl moiety, which is generated by SPS1 and SPS2, in FBN5-B/SPS homodimeric complexes stimulates the enzyme activity of SPS1 and SPS2.     

The roles of two novel FBN1 gene mutations in the genotype-phenotype correlations of Marfan syndrome and ectopia lentis patients with marfanoid habitus

Mutations in the fibrillin-1 (FBN1) gene have been identified in patients with Marfan syndrome (MFS) and Marfan-like connective tissue disorders. In this study, two Chinese families were recruited. The patients in family 1 were well characterized with MFS, while those in family 2 displayed Marfan-like disorders such as ectopia lentis (EL) and marfanoid habitus, but did not develop cardiovascular diseases. We aimed to analyze the pathogenic mutations and their relationships with phenotypes in these two Chinese families. All participants underwent complete physical, ophthalmic, and cardiovascular examinations. The 65 exons and flanking intronic sequences of FBN1 were amplified by polymerase chain reaction, and screened for mutations by denaturing high-performance liquid chromatography and sequencing. One hundred and fifteen unrelated controls were analyzed using the same methods to confirm the mutations. In family 1, we identified the mutation p.C499S in the calcium-binding epidermal growth factor (cbEGF)-like domain 3 of FBN1. In family 2, the mutation p.C908Y was identified in an interdomain region of the hybrid motif 2 linked to the cbEGF-like domain 10. It can be concluded that FBN1 mutations involving cysteine substitutions are usually associated with MFS and EL with some MFS features. Moreover, pathology seemed more serious when the mutations disrupted the three disulfide bridges in the cbEGF-like domains, which was more likely to cause typical MFS than if the mutations occurred in the hybrid motifs. Our data preliminarily establish a genotype-phenotype correlation in the diagnostic process of MFS and predominant EL with Marfan-like features.     

汉族马凡综合征(MFS)患者FBN1基因两种新发突变分析

为调查马凡综合征(Marfan syndrome, MFS)患者的原纤维蛋白-1(Fibrillin-1, FBN1)基因突变情况, 应用聚合酶链反应(PCR)和变性高效液相色谱法(Denaturing high-performance liquid chromatography, DHPLC)对MFS患者的FBN1基因进行突变筛查, 对DHPLC初筛异常的DNA片段进行测序分析。结果在两个MFS家系中发现FBN1基因两种新的突变: 一种为复合突变包含第55号外显子的缺失突变c.6862_6871delGGCTGTGTAG (p.Gly2288MetfsX109)、同义突变c.6861A>G和内含子的突变c.[6871+1_6871+11delGTAAGAGGATC; 6871+34dupCATCAGAAGTGACAGTGGACA]; 另一种为第20号外显子的错义突变c.2462G>A(p.Cys821Tyr)。研究表明, FBN1基因的缺失突变c.[6862_6871delGGCTGTGTAG; 6871+1_6871+11delGTAAGAGGATC] (p.Gly2288MetfsX109)和错义突变c.2462G>A(p.Cys821Tyr)可能分别是这两个家系患者的致病原因。     

A Point Mutation Creating an ExtraN-Glycosylation Site in Fibrillin-1 Results in Neonatal Marfan Syndrome

Fibrillin-1 is a large cysteine-rich glycoprotein of the 10-nm microfibrils in the extracellular matrix. A spectrum of mutations in the fibrillin-1 gene (FBN1) have been identified in patients with Marfan syndrome (MFS), and the majority of mutations resulting in the neonatal and often lethal form of MFS have been identified in the restricted region of exons 24–32 of theFBN1gene. Here we report a novel point mutation in exon 25 of theFBN1gene in a patient with lethal MFS. The mutation resulted in a molecular defect rarely encountered in human diseases, the creation of an extra consensus sequence forN-glycosylation. Metabolic labeling of the patient fibroblast culture andin vitroexpression of the mutagenized cDNA construct suggest that this novelN-glycosylation site is actually utilized. Immunohistochemical and ultrastructural analyses of the fibroblast cultures of the patient show that this excessiveN-glycosylation severely affects microfibril formationin vitro;this finding emphasizes the importance of correct posttranslational modifications of fibrillin molecules for correct aggregation into microfibrillar structures.     

中国汉族两个马凡综合征家系FBN1基因的一个新插入突变和一个复发点突变

目的:明确两个中国北方汉族马凡综合征(Marfan syndrome,MFS)家系的临床特点,并对其进行基因诊断。方法:对两个家系进行家系调查和系谱分析,应用聚合酶链式反应-DNA测序方法对原纤维蛋白1基因(Fibrillin-1,FBN1)的所有外显子进行测序。应用Swiss-model、Polyphen-2和SIFT软件对发现的变异位点进行功能预测。结果:两个家系均呈常染色显性遗传特点,在家系1患者中发现一个新的插入突变,即第13外显子1691位碱基处插入碱基A(1691 ins A),导致蛋白在第571位氨基酸处翻译提前终止。此外,在家系2患者中发现一个已知的点突变,即第27外显子第3463位碱基由G变为A(3463 GA),导致第1155位氨基酸由天冬氨酸变为天冬酰胺。这两个变异位点在家系的健康人及50例健康对照中均未出现。功能预测发现这两个变异位点均可能会影响FBN1蛋白的结构或功能。结论:在两个MFS家系中发现一个新插入突变位点(1691 ins A)和一个已知点突变位点(3463 GA),为扩大FBN1基因的突变谱及进一步阐明FBN1基因突变在MFS中的作用提供理论依据。     

Application of next-generation sequencing to screen for pathogenic mutations in 123 unrelated Chinese patients with Marfan syndrome or a related disease

Marfan syndrome(MFS) is a systemic connective tissue disease principally affecting the ocular, skeletal and cardiovascular systems. This autosomal dominant disorder carries a prevalence of 1:3,000 to 1:5,000. This study aims to define the mutational spectrum of MFS related genes in Chinese patients and to establish genotype-phenotype correlations in MFS. Panel-based targeted next-generation sequencing was used to analyze the FBN1, TGFBR1 and TGFBR2 genes in 123 unrelated Chinese individuals with MFS or a related disease. Genotype-phenotype correlation analyses were performed in mutation-positive patients. The results showed that 97 cases/families(78.9%; 97/123) harbor at least one(likely) pathogenic mutation, most of which were in FBN1; four patients had TGFBR1/2 mutations; and one patient harbored a SMAD3 mutation. Three patients had two FBN1 mutations, and all patients showed classical MFS phenotypes. Patients with a dominant negative-FBN1 mutation had a higher prevalence of ectopia lentis(EL). Patients carrying a haploinsufficiency-FBN1 mutation tended to have aortic dissection without EL. This study extends the spectrum of genetic backgrounds of MFS and enriches our knowledge of genotype-phenotype correlations.     

ENU Mutagenesis Reveals a Novel Phenotype of Reduced Limb Strength in Mice Lacking Fibrillin 2

Background

Fibrillins 1 (FBN1) and 2 (FBN2) are components of microfibrils, microfilaments that are present in many connective tissues, either alone or in association with elastin. Marfan''s syndrome and congenital contractural arachnodactyly (CCA) result from dominant mutations in the genes FBN1 and FBN2 respectively. Patients with both conditions often present with specific muscle atrophy or weakness, yet this has not been reported in the mouse models. In the case of Fbn1, this is due to perinatal lethality of the homozygous null mice making measurements of strength difficult. In the case of Fbn2, four different mutant alleles have been described in the mouse and in all cases syndactyly was reported as the defining phenotypic feature of homozygotes.

Methodology/Principal Findings

As part of a large-scale N-ethyl-N-nitrosourea (ENU) mutagenesis screen, we identified a mouse mutant, Mariusz, which exhibited muscle weakness along with hindlimb syndactyly. We identified an amber nonsense mutation in Fbn2 in this mouse mutant. Examination of a previously characterised Fbn2-null mutant, Fbn2^fp, identified a similar muscle weakness phenotype. The two Fbn2 mutant alleles complement each other confirming that the weakness is the result of a lack of Fbn2 activity. Skeletal muscle from mutants proved to be abnormal with higher than average numbers of fibres with centrally placed nuclei, an indicator that there are some regenerating muscle fibres. Physiological tests indicated that the mutant muscle produces significantly less maximal force, possibly as a result of the muscles being relatively smaller in Mariusz mice.

Conclusions

These findings indicate that Fbn2 is involved in integrity of structures required for strength in limb movement. As human patients with mutations in the fibrillin genes FBN1 and FBN2 often present with muscle weakness and atrophy as a symptom, Fbn2-null mice will be a useful model for examining this aspect of the disease process further.     

Identification of an FBN1 mutation in bovine Marfan syndrome-like disease

Mutations in the gene encoding fibrillin-1 (FBN1), a component of the extracellular microfibril, cause Marfan syndrome (MFS). Frequent observation of cattle with a normal withers height, but lower body weight than age-matched normal cattle, was recently reported among cattle sired by phenotypically normal Bull A, in Japanese Black cattle. These cattle also showed other characteristic features similar to the clinical phenotype of human MFS, such as a long phalanx proximalis, oval face and crystalline lens cloudiness. We first screened a paternal half-sib family comprising 36 affected and 10 normal offspring of Bull A using the BovineSNP50 BeadChip (illumina). Twenty-two microsatellite markers mapped to a significant region on BTA10 were subsequently genotyped on the family. The bovine Marfan syndrome-like disease (MFSL) was mapped onto BTA10. As FBN1 is located in the significant region, FBN1 was sequenced in Bull A, and three affected and one normal cattle. A G>A mutation at the intron64 splicing accepter site (c.8227-1G>A) was detected in 31 of 36 affected animals (84.7%). The c.8227-1G>A polymorphism was not found in 20 normal offspring of Bull A or in 93 normal cattle unrelated to Bull A. The mutation caused a 1-base shift of the intron64 splicing accepter site to the 3' direction, and a 1-base deletion in processed mRNA. This 1-base deletion creates a premature termination codon, and a 125-amino acid shorter Fibrillin-1 protein is produced from the mutant mRNA. We therefore conclude that the c.8227-1G>A mutation is causative for MFSL. Furthermore, it was suggested that Bull A exhibited germline mosaicism for the mutation, and that the frequency of the mutant sperm was 14.9%.     

Ung1p-mediated uracil-base excision repair in mitochondria is responsible for the petite formation in thymidylate deficient yeast

The budding yeast CDC21 gene, which encodes thymidylate synthase, is crucial in the thymidylate biosynthetic pathway. Early studies revealed that high frequency of petites were formed in heat-sensitive cdc21 mutants grown at the permissive temperature. However, the molecular mechanism involved in such petite formation is largely unknown. Here we used a yeast cdc21-1 mutant to demonstrate that the mutant cells accumulated dUMP in the mitochondrial genome. When UNG1 (encoding uracil-DNA glycosylase) was deleted from cdc21-1, we found that the ung1Δ cdc21-1 double mutant reduced frequency of petite formation to the level found in wild-type cells. We propose that the initiation of Ung1p-mediated base excision repair in the uracil-laden mitochondrial genome in a cdc21-1 mutant is responsible for the mitochondrial petite mutations.