Fibrillin-1 mutations in Marfan syndrome and other type-1 fibrillinopathies

Fibrillin is the major component of extracellular microfibrils and is widely distributed in connective tissue throughout the body. Mutations in the fibrillin-1 FBN1) gene, on chromosome 15q21.1, have been found to cause Marfan syndrome, a dominantly inherited disorder characterised by clinically variable skeletal, ocular, and cardiovascular abnormalities. Fibrillin-1 mutations have also been found in several other related connective tissue disorders, such as severe neonatal Marfan syndrome, dominant ectopia lentis, familial ascending aortic aneurysm, isolated skeletal features of Marfan syndrome, and Shprintzen-Goldberg syndrome. Mutations are spread throughout the gene and, with the exception of neonatal Marfan syndrome, show no obvious clustering or phenotypic association. Hum Mutat 10:415–423, 1997. © 1997 Wiley-Liss, Inc.     

Identification of 9 novel FBN1 mutations in German patients with Marfan syndrome

We report 9 new mutations in German patients presenting with classical Marfan syndrome. All mutations occur in exons with calcium‐binding (cb) epidermal growth factor‐like (EGF) domains. Five mutations are missense involving exons 12, 27, 30, 44, and 52 with the resultant substitution of cysteine by phenylalanine (C504F), cysteine by tyrosine (C1129Y), tyrosine by cysteine (Y1261C), cysteine by serine (C1833S), and cysteine by tyrosine (C2142Y), respectively. The other four mutations are single base deletions in exons 39, 43, 48, and 58, at nucleotide A4826, C5311, T6018, and A7291, respectively, each resulting in frameshift with premature termination. Four mutations were detected in sporadic cases and are likely to be de novo. Hum Mutat 14:181, 1999. © 1999 Wiley‐Liss, Inc.     

Mutations of FBN1 and genotype-phenotype correlations in Marfan syndrome and related fibrillinopathies

The Marfan syndrome (MFS) is a pleiotropic, autosomal dominant disorder of connective tissue with highly variable clinical manifestations including aortic dilatation and dissection, ectopia lentis, and a series of skeletal anomalies. Mutations in the gene for fibrillin-1 (FBN1) cause MFS, and at least 337 mainly unique mutations have been published to date. FBN1 mutations have been found not only in MFS but also in a range of connective tissue disorders collectively termed fibrillinopathies ranging from mild phenotypes, such as isolated ectopia lentis, to severe disorders including neonatal MFS, which generally leads to death within the first two years of life. The present article intends to provide an overview of mutations found in MFS and related disorders and to discuss potential genotype-phenotype correlations in MFS.     

FBN1 mutation screening of patients with Marfan syndrome and related disorders: detection of 46 novel FBN1 mutations

Fibrillin-1 gene ( FBN1 ) mutations cause Marfan syndrome (MFS), an inherited connective tissue disorder with autosomal dominant transmission. Major clinical manifestations affect cardiovascular and skeletal apparatuses and ocular and central nervous systems. We analyzed FBN1 gene in 99 patients referred to our Center for Marfan Syndrome and Related Disorders (University of Florence, Florence, Italy): 85 were affected by MFS and 14 by other fibrillinopathies type I. We identified mutations in 80 patients. Among the 77 different mutational events, 46 had not been previously reported. They are represented by 49 missense (61%), 1 silent (1%), 13 nonsense (16%), 6 donor splice site mutations (8%), 8 small deletions (10%), and 3 small duplications (4%). The majority of missense mutations were within the calcium-binding epidermal growth factor-like domains. We found preferential associations between The Cys-missense mutations and ectopia lentis and premature termination codon mutations and skeletal manifestations. In contrast to what reported in literature, the cardiovascular system is severely affected also in patients carrying mutations in exons 1–10 and 59–65. In conclusion, we were able to detect FBN1 mutations in 88% of patients with MFS and in 36% of patients with other fibrillinopathies type I, confirming that FBN1 mutations are good predictors of classic MFS.     

Eight novel mutations of the FBN1 gene found in Japanese patients with Marfan syndrome

Marfan syndrome (MFS), an autosomal dominant connective tissue disorder, is caused by mutations in the gene encoding fibrillin 1 (FBN1). The clinical spectrum and severity of MFS disorder varies greatly both between and within families. Since there have been only a few reports on the relationship between FBN1 genotypes and clinical phenotypes in Japanese patients, the FBN1 gene was analyzed in 27 Japanese patients diagnosed with MFS. The nucleotide sequence of the 65 exons of the FBN1 gene was analyzed by PCR and direct sequencing. We have identified six polymorphisms and nine mutations including: four missense mutations (C1652Y, Q2054P, D2127Y, C2221R) in six patients, three nonsense mutations (R215X, S813X, R2220X) in three patients, and two frameshift mutations (2567insT, 7790insT) in three patients. Six of these nine mutations were in the calcium-binding epidermal growth factor-like domains all causative mutations detected except for C2221R were novel. It has been reported that the severe phenotypes of infantile MFS correlate with mutations in the mid region of FBN1, however, mutations were not detected in this region in the population analyzed in this study. Our results suggest that the location of the mutation is not the sole determinant of phenotypic severity; rather there is some difference in the genetic basis of MFS between Japanese and Caucasian populations.     

Characterisation of four novel fibrillin-1 (FBN1) mutations in Marfan syndrome.

Forty-four percent of the fibrillin-1 gene (FBN1) from 19 unrelated families with Marfan syndrome was screened for putative mutations by single strand conformational polymorphism (SSCP) analysis. Four novel mutations were identified and characterised in five people, three with classical Marfan syndrome (two from one family, and one from an unrelated family), one with a more severe phenotype, and one with neonatal Marfan syndrome. The base substitutions G2113A, G2132A, T3163G, and G3458A result in amino acid substitutions A705T, C711Y, C1055G, and C1152Y, respectively. C711Y, C1055G, and C1152Y lead to replacement of a cysteine by another amino acid; the latter two occur within epidermal growth factor-like motifs in exon 25 and 27, respectively. The A705T mutation occurs at exon 16 adjacent to the GT splice site. The A705T and C711Y mutations, at exon 16 and 17, respectively, are the first documented in the second transforming growth factor-beta 1 binding protein-like motif of FBN1.     

Detection of six novel FBN1 mutations in British patients affected by Marfan syndrome

Marfan syndrome (MFS), an autosomal dominant disorder of the extracellular matrix, is due to mutations in fibrillin-1 (FBN1) gene. Investigations carried out in the last decade, unveiled the unpredictability of the site of the mutation, which could be anywhere in the gene. FBN1 mutations have been reported in a spectrum of diseases related to MFS, with no clear evidence for a phenotype-genotype correlation. In this paper we analysed 10 British patients affected by MFS and we were able to characterise five novel missense mutations (C474W, C1402Y, G1987R, C2153Y, G2536R), one novel frameshift mutation (7926delC), one already described mutation (P1424A) and one FBN1 variant (P1148A) classified as a polymorphism in the Asian population. Four out of the five novel missense mutations involved either cysteines or an amino acid conserved in the domain structure. The mutation yield in this study is calculated at 80.0% (8/10), thus indicating that SSCA is a reliable and cost-effective technique for the screening of such a large gene. Our results suggest that this method is reliable to search for FBN1 mutations and that FBN1 screening could be a helpful tool to confirm and possibly anticipate the clinical diagnosis in familial cases. Hum Mutat 18:251, 2001.     

Detection of thirty novel FBN1 mutations in patients with Marfan syndrome or a related fibrillinopathy

Marfan syndrome (MFS) is a disorder of the extracellular matrix caused by mutations in the gene encoding fibrillin-1 (FBN1). Recent studies have illustrated the variability in disease severity and clinical manifestations of MFS. Useful genotype-phenotype correlations have been slow to emerge. We screened 57 unrelated patients with MFS or a Marfan-like phenotype using a combination of SSCP and/or DHPLC. We detected 49 different FBN1 mutations, 30 (62%) of which were novel. The mutations comprised 38 substitutions (78%), 10 deletions (20%), and one duplication (2%). There were 28 missense (57%), nine frameshift (18%), eight splice site (16%), and four nonsense mutations (8 %). Genotype-phenotype analysis revealed that patients with an identified FBN1 mutation were more likely to have ectopia lentis and cardiovascular complications compared to those without an identifiable mutation (relative risks of 4.6 and 1.9, respectively). Ectopia lentis was also found to be more prevalent in patients whose mutations involved a cysteine substitution (relative risk 1.6) and less prevalent in those with premature termination mutations (relative risk 0.4). In our hands, we achieved 93% mutation detection for DHPLC analysis of patients who fulfilled the Ghent criteria. Further analysis of detailed clinical information and mutation data may help to anticipate the clinical consequences of specific FBN1 mutations.     

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.     

Fibrillin gene (FBN1) mutations in Japanese patients with Marfan syndrome

Marfan syndrome (MFS; MIM #154700) is a connective tissue disorder characterized by cardiovascular, skeletal, and ocular abnormalities. The fibrillin-1 gene (FBN1; MIM no. 134797) on chromosome 15 was revealed to be the cause of Marfan syndrome. To date over 137 types of FBN1 mutations have been reported. In this study, two novel mutations and a recurrent de-novo mutation were identified in patients with MFS by means of single-strand conformational polymorphism (SSCP) analysis. The two novel mutations are a 4-bp deletion at nucleotide 2820-2823 and a G-to-T transversion at nucleotide 1421 (C474F), located on exon 23 and exon 11, respectively. A previously reported mutation at the splicing donor site of intron 2 (IVS2 G + 1A), which is predicted to cause exon skipping, was identified in a sporadic patient with classical MFS. Received: November 1, 1999 / Accepted: November 9, 1999     

Classic, atypically severe and neonatal Marfan syndrome: twelve mutations and genotype-phenotype correlations in FBN1 exons 24-40

Mutations in the gene for fibrillin-1 (FBN1) cause Marfan syndrome, an autosomal dominant disorder of connective tissue with prominent manifestations in the skeletal, ocular, and cardiovascular system. There is a remarkable degree of clinical variability both within and between families with Marfan syndrome as well as in individuals with related disorders of connective tissue caused by FBN1 mutations and collectively termed type-1 fibrillinopathies. The so-called neonatal region in FBN1 exons 24-32 comprises one of the few generally accepted genotype-phenotype correlations described to date. In this work, we report 12 FBN1 mutations identified by temperature-gradient gel electrophoresis screening of exons 24-40 in 127 individuals with Marfan syndrome or related disorders. The data reported here, together with other published reports, document a significant clustering of mutations in exons 24-32. Although all reported mutations associated with neonatal Marfan syndrome and the majority of point mutations associated with atypically severe presentations have been found in exons 24-32, mutations associated with classic Marfan syndrome occur in this region as well. It is not possible to predict whether a given mutation in exons 24-32 will be associated with classic, atypically severe, or neonatal Marfan syndrome.     

Two novel and one known mutation of the TGFBR2 gene in Marfan syndrome not associated with FBN1 gene defects

TGF-beta-receptor 2 (TGFBR2) gene defects have been recently associated with Marfan syndrome (MFS) with prominent cardio-skeletal phenotype in patients with negative fibrillin-1 (FBN1) gene screening. Four mutations have been identified to date in five unrelated families. We screened TGFBR2 gene by direct automated sequencing in two adult patients diagnosed with MFS according to Ghent criteria, and in one girl clinically suspected as affected on the basis of a major cardiovascular criterion and skeletal involvement, all proven not to carry mutations in the exon-intron boundaries of FBN1 gene. We identified two novel and one known TGFBR2 gene mutations in the three unrelated probands. The D446N was identified in a 4-year-old girl with de novo disease characterized by severe cardiovascular disease and skeletal involvement. The M425V and R460H mutations were identified in two familial, autosomal dominant MFSs, both characterized by major cardio-skeletal signs and absence of major ocular signs. The mutation R460H has been recently reported in a family with thoracic aortic aneurysms and dissection. The three mutations are absent in 192 controls and affect evolutionarily conserved residues of the serine/threonine kinase domain (exon 5). Our data support the recently reported association between TGFBR2 gene and MFS without major ocular signs (MFS2). The number of genotyped cases however is too low to confirm that major ocular signs are characteristically absent in MFS2. Accordingly, all patients proven or suspected to be affected by MFS with negative FBN1 gene screening could benefit from rapid investigation of the TGFBR2 gene.     

FBN1新生突变引起的马凡综合征及其基因型-表型的关联研究

 目的: 本研究对2个不同马凡综合征(Marfan syndrome)的小家系进行致病基因FBN1的编码区和剪切位点突变检测,以寻找致病的突变,并初步探索马凡综合征基因型-表型的关联。方法: 通过临床检查、实验室检查及心脏超声检查确诊2个无血缘关系的家庭中原疑似为马凡综合征的3例患者。运用新一代测序对家系1的疑似患者行FBN1基因的全外显子组测序,并对检出的致病性遗传变异进行Sanger验证及在所有家系成员中验证;对于家系2的存活成员,本研究直接进行PCR扩增FBN1基因的所有编码区及剪切位点,对产物进行直接Sanger测序。另外在50个正常对照中对新发现的突变位点进行基于PCR产物的测序分析,以排除多态性;并对实验结果行生物信息学分析。结果: 所有存活的疑似患者均确诊为马凡综合征。在家系1中,我们检测到了一个FBN1基因数据库中尚未报道的新突变c.4685G>A(p.Cys1562Tyr),并且患者父母和同胞姐姐均未检测到此变异,故此突变为一个新生突变。该错义突变使第1562位上极性中性的含硫的半胱氨酸被极性中性的含羟苯基的酪氨酸所替代,影响了fibrillin-1蛋白一个TGF-β结合结构域,导致蛋白质的二级结构发生改变。家系2含父母及一对同卵双胎患者,其中一患者已去世。我们在存活患者检测到1个FBN1基因的已报道致病突变c.3706T>C(p.Cys1236Arg),该突变在患者父母中不存在,故也为新生突变。结论: 本文报道了一例FBN1基因的新突变及另一例由FBN1基因已知突变引起的马凡综合征,二者皆为新生突变,并在家系中进行了基因型-表型的比较,表明家系1的新突变可能与经典马凡综合征的表型相关,而家系2的已知突变确和新生儿重症马凡综合征表型相关。     

Marfan syndrome caused by a novel FBN1 mutation with associated pigmentary glaucoma

Mutations in fibrillin‐1 (FBN1) cause a wide spectrum of disorders, including Marfan syndrome, which have in common defects in fibrillin‐1 microfibrils. Ectopia lentis and myopia are frequently observed ocular manifestations of Marfan syndrome. Glaucoma is also associated with Marfan syndrome, though the form of glaucoma has not been well‐characterized. In this report, ocular examination of a patient diagnosed with Marfan syndrome based on family history and aortic dilatation was performed, including measurement of facility of aqueous humor outflow by tonography. The patient did not have ectopia lentis at the age of 42 years. Based on optic nerve appearance, reduced outflow facility, elevated IOP with open angles and clear signs of pigment dispersion, the patient was diagnosed with pigmentary glaucoma. The patient was heterozygous for a novel truncating mutation in FBN1, p.Leu72Ter. Histology of normal human eyes revealed abundant expression of elastic fibers and fibrillin‐1 in aqueous humor outflow structures. This is the first report of a patient with Marfan syndrome that is caused by a confirmed FBN1 mutation with associated pigmentary glaucoma. In addition to identifying a novel mutation of FBN1 and broadening the spectrum of associated ocular phenotypes in Marfan syndrome, our findings suggest that pigmentary glaucoma may involve defects in fibrillin‐1 microfibrils. © 2013 Wiley Periodicals, Inc.     

Evaluation and application of denaturing HPLC for mutation detection in Marfan syndrome: Identification of 20 novel mutations and two novel polymorphisms in the FBN1 gene

Mutations in the human fibrillin 1 gene (FBN1) cause the Marfan syndrome (MFS), an autosomal dominant connective tissue disorder. Knowledge about FBN1 mutations is important for early diagnosis, management, and genetic counseling. However, mutation detection in FBN1 is a challenge because the gene is very large in size ( approximately 200 kb) and the approximately 350 mutations detected so far are scattered over 65 exons. Conventional methods for large-scale detection of mutations are expensive, technically demanding, or time consuming. Recently, a high-capacity low-cost mutation detection method was introduced based on denaturing high-performance liquid chromatography (DHPLC). To assess the sensitivity and specificity of this method, we blindly screened 64 DNA samples of known FBN1 genotype exon-by-exon using exon-specific DHPLC conditions. Analysis of 682 PCR amplicons correctly identified 62 out of 64 known sequence variants. In three MFS patients of unknown FBN1 genotype, we detected two mutations and eight polymorphisms. Overall, 20 mutations and two polymorphisms are described here for the first time. Our results demonstrate 1) that DHPLC is a highly sensitive (89-99%, P = 0.05) method for FBN1 mutation detection; but 2) that chromatograms with moderate and weak pattern abnormalities also show false positive signals (in all 45-59%, P = 0.05); 3) that the difference in the chromatograms of heterozygous and homozygous amplicons is mostly independent of the type of sequence change; and 4) that DHPLC column conditions, additional base changes, and the amounts of injected PCR products influence significantly the shape of chromatograms. A strategy for FBN1 mutation screening is discussed.     

Prevalence of dural ectasia in 63 gene-mutation-positive patients with features of Marfan syndrome type 1 and Loeys-Dietz syndrome and report of 22 novel FBN1 mutations

Marfan syndrome is an autosomal dominant disorder involving different organ systems. Marfan syndrome type 1 (MFS1) is caused by mutations in the FBN1 gene. Heterozygosity for mutations in the TGFBR1 or TGFBR2 genes cause Loeys–Dietz syndrome (LDS) types 2A and 2B that overlap with MFS1 in their clinical features. The phenotype of MFS1 is defined by the Ghent nosology, which classifies the clinical manifestations in major and minor criteria. Dural ectasia is one of the major criteria for Marfan syndrome but it is rarely tested for. We here report 22 novel and 9 recurrent mutations in the FBN1 gene in 36 patients with clinical features of Marfan syndrome. Sixty patients with identified mutations in the FBN1 gene and three patients with mutations in the TGFBR1 or TGFBR2 genes were examined for dural ectasia. Forty-seven of the 60 patients (78%) with MFS1 showed the dural ectasia criterion and 13 (22%) did not. Thirty-three (55%) patients were suspected of having Marfan syndrome and 24 (73%) of them had dural ectasia. Two of the three patients with LDS had dural ectasia.     

Search for correlations between FBN1 genotype and complete Ghent phenotype in 44 unrelated Norwegian patients with Marfan syndrome

In monogenic disorders, correlation between genotype and phenotype is a premise for predicting prognosis in affected patients. Predictive genetic testing may enable prophylaxis and promote clinical follow-up. Although Marfan syndrome (MFS) is known as a monogenic disorder, according to the present diagnostic criteria a mutation in the gene FBN1 is not sufficient for the diagnosis, which also depends on the presence of a number of clinical, radiological, and other findings. The fact that MFS patient cohorts only infrequently have been examined for all relevant phenotypic manifestations may have contributed to inconsistent reports of genotype-phenotype correlations. In the Norwegian Study of Marfan syndrome, all participants were examined for all findings contained in the Ghent nosology by the same investigators. Mutation identification was carried out by robot-assisted direct sequencing of the entire FBN1 coding sequence and MLPA analysis. A total of 46 mutations were identified in 44 unrelated patients, all fulfilling Ghent criteria. Although no statistically significant correlation could be obtained, the data indicate associations between missense or splice site mutations and ocular manifestations. While mutations in TGF-domains were associated with the fulfillment of few major criteria, severe affection was indicated in two cases with C-terminal mutations. Intrafamilial phenotypic variation among carriers of the same mutation, suggesting the influence of epigenetic facors, complicates genetic counseling. The usefulness of predictive genetic testing in FBN1 mutations requires further investigation.