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

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.

Thumb duplication: molecular analysis of different clinical types

PURPOSE

Molecular analysis of different types of thumb duplication and identification of new suspected gene mutations.

MATERIALS AND METHODS

In a series of patients operated for polydactyly, DNA was extracted from blood samples collected preoperatively. Among these, the samples of two patients with thumb duplication (Wassel types III and IV) were initially selected for molecular analysis. The method of Clinical Exome Solution was used for the study of the phenotype-involved genes. Next-generation sequencing (NGS) was performed on a NextSeq-500 Platform (Illumina), and Sophia DDM^® SaaS algorithms were used for the bioinformatics analysis of the data.

RESULTS

In total, 8-including 4 new-mutations were detected in CEP290 (1 mutation), RPGRIP1 (2 mutations), TMEM216 (2 mutations), FBN1 (1 mutation), CEP164 (1 mutation), and MEGF8 (1 mutation) genes. NGS revealed 3 mutated genes in the patient with Wassel III thumb duplication and 5 mutated genes in the patient with Wassel IV duplication. The molecular analysis revealed that the patients had 2 mutated genes in common, but they only shared one common mutation.

CONCLUSION

The new detected mutations are most probably associated with thumb duplication, as they belong to genes with already described mutations causing ciliopathies, often including polydactyly in their phenotype. Recognition of these mutations will be helpful to prenatal diagnosis, operative treatment strategy prediction, and possible future experimental applications in gene therapy.

Variable severity of cardiovascular phenotypes in patients with an early-onset form of Marfan syndrome harboring FBN1 mutations in exons 24-32

A subgroup of patients with Marfan syndrome (MFS) who have mutations in exons 24-32 of the FBN1 gene manifests severe atrioventricular valve insufficiency and skeletal problems as early as the neonatal period. These patients usually die in the first 2 years of life, thus a region between exons 24 and 32 of FBN1 is recognized as a critical region for this neonatal form of MFS (nMFS). Here, we report five consecutive patients who manifested a cardiovascular phenotype until infancy with mutations in the critical region for nMFS. Although three of these patients showed severe mitral regurgitation and died before reaching 1 year of age, the remaining two patients survived for over 5 years under medical and/or surgical interventions. Two splicing mutations and one missense mutation were identified in the three deceased patients, whereas two missense mutations were found in the two survivors. Currently, the clinical severity of patients with early-onset MFS harboring mutations in the critical region for nMFS seem to be more variable than ever thought, and intensive treatments are recommended even in this subgroup of patients with MFS.

Dural ectasia in Marfan syndrome: a case control study

BACKGROUND AND PURPOSE

Dural ectasia (DE) is one of the major criteria of Marfan syndrome (MFS). Our aim was to establish the prevalence of DE in an adult population fulfilling the Ghent criteria for MFS and to assess definitions of DE.

MATERIALS AND METHODS

One hundred five adults with suspected MFS were included. MR imaging at 1.5T was performed unless contraindicated; then CT was obtained. Lumbosacral anteroposterior vertebral body diameters (VBD) and dural sac diameters (DSD) were measured. Dural sac ratios (DSR = DSD/VBD) at levels L3 through S1 were calculated. Anterior meningoceles, herniations of nerve root sleeves, and scalloping were characterized. One hundred one sex- and age-matched patients were included as controls.

RESULTS

We identified 3 patient groups: 1) fulfilling Ghent criteria independent of DE (n = 73), 2); fulfilling Ghent criteria dependent on DE (n = 14), and 3); and suspected MFS, not fulfilling Ghent criteria (n = 18). DE was found in 86% of group 1. At levels L4-S1, mean DSRs were significantly higher in group 1 than in group 3 and controls (P < .001). Herniations of the nerve root sleeves were present in 73% in group 1 versus 1% in controls. Anterior meningoceles were found in 37% and 14% in groups 1 and 2, respectively, but not in group 3 or controls.

CONCLUSIONS

The diagnosis of DE on MR imaging or CT should be based on the presence of at least 1 of the following criteria: anterior meningoceles or nerve root sleeve herniation, DSD at S1 or below larger than DSD at L4, and DSR at S1 >0.59.

Histopathology and fibrillin-1 distribution in severe early onset Marfan syndrome

Marfan syndrome (MFS) is an autosomal dominant condition which may involve the cardiovascular, ocular, skeletal, and other systems. Mutations causing MFS are found in the FBN1 gene, encoding fibrillin-1, an extracellular matrix protein involved in microfibril formation. In the most severe cases, mutations are generally found in exons 24-32, and children with these mutations usually die in the first years of life, of cardiopulmonary failure. We present clinical, molecular and histopathological studies on a patient with severe early onset MFS. He has a mutation in exon 25 of FBN1, a G>A transition at nucleotide position 3131 that converts the codon TGC, coding for cysteine at position 1044, to TAC, coding for tyrosine (C1044Y). This has resulted in abnormalities of the extracellular matrix and a severe clinical phenotype, although he has survived to the age of 14 years.

Do extracellular matrix protein expressions change with cyclic reproductive hormones in pelvic connective tissue from women with stress urinary incontinence?

BACKGROUND

To evaluate differential expression of transforming growth factor (TGF-beta1), latent transforming factor-binding proteins (LTBP-1, LTBP-2) and elastin microfibril components (fibrillin-1 and fibrillin-2) in vaginal tissue from women with stress urinary incontinence (SUI).

METHODS

In this case-control study, vaginal tissue from women in both phases of the menstrual cycle was obtained. Messenger RNA (mRNA) expressions of LTBP-1, LTBP-2, fibrillin-1, fibrillin-2 and TGF-beta1 were determined by relative real-time quantification PCR. Tissue localization was analysed by immunohistochemistry, and semiquantitative protein expression was evaluated by Western blot analysis.

RESULTS

Vaginal wall fibroblasts synthesized all proteins tested. LTBP-1, LTBP-2 and TGF-beta1 co-localized with elastin microfibrils, fibrillin-1 and fibrillin-2 in the extracellular matrix. LTBP-1 mRNA and protein expressions were higher in control versus women affected with SUI in the proliferative phase (P = 0.04), while in the secretory phase, mRNA expression in cases was higher (P = 0.04). Fibrillin-1 mRNA was higher in women affected by SUI versus controls in both phases, but no statistical differences in fibrillin-1 protein expression were observed between the two groups in either phase. LTBP-2 and TGF-beta1 mRNA expressions showed the same trends as LTBP-1.

CONCLUSION

LTBP-1, LTBP-2, TGF-beta1, fibrillin-1, and fibrillin-2 expressions are hormonally regulated in vaginal wall fibroblasts and differ in women affected by SUI when compared to controls. These data suggest a mechanism to regulate TGF-beta1 activity in pelvic connective tissue.

Molecular genetics of Marfan syndrome

PURPOSE OF REVIEW

Marfan syndrome, the founding member of connective tissue disorders, is characterized by involvement of three major systems (skeletal, ocular, and cardiovascular) due to alteration in microfibrils. FBN1 at 15q21.1 was found to cause Marfan syndrome in 1991, and in 2004 TGFBR2 at 3p24.1 was newly identified as the Marfan syndrome type II gene. Several studies implied that fibrillin-1 and transforming growth factor-beta (TGF-beta) signaling are functionally related in extracellular matrix. Identification of TGFBR2 mutations in Marfan syndrome type II provided the direct evidence of the relation in humans.

RECENT FINDINGS

More than 500 FBN1 mutations have been found in Marfan syndrome, tentative genotype - phenotype correlations have emerged, and mouse models are providing insight into pathogenic mechanisms. TGFBR2 mutations are still limited, however, in 2005 were also reported to cause a new aneurysm syndrome. Functional association between fibrillin-1 and TGF-beta signaling in extracellular matrix has been presented.

SUMMARY

This review focuses on recent molecular genetics advances in Marfan syndrome and overlapping connective tissue disorders. Mutation spectrum of FBN1 and TGFBR2 in relation to phenotype is presented. Functional relation between fibrillin-1 and TGF-beta signaling is discussed. Future prospects in the study of Marfan syndrome are presented.

Ectopia lentis phenotypes and the FBN1 gene

Mutations of the fibrillin-1 (FBN1) gene on chromosome 15 have been described in patients with classical Marfan syndrome (MFS), neonatal MFS, the "MASS" phenotype, autosomal dominant ascending aortic aneurysms, autosomal dominant ectopia lentis (EL), Marfanoid skeletal features [Milewicz et al., 1995: J Clin Invest 95:2373-2378], familial arachnodactyly, Shprintzen-Goldberg syndrome [Hayward et al., 1994: Mol Cell Probes 8:325-327; Furthmayr and Francke, 1997: Semin Thorac Cardiovasc Surg 9:191-205], and severe progressive kyphoscoliosis [Adès et al., 2002: Am J Med Genet 109:261-270]. We report the use of denaturing high performance liquid chromatography (DHPLC) to facilitate the characterization of a previously elusive FBN1 mutation in the large autosomal dominant EL kindred described by Edwards et al. [1994: Am J Med Genet 53:65-71]. This isolated EL kindred remains the largest for which detailed clinical data is available. Nine years on, we present an update of the clinical status of the family. We report a recurrent FBN1 mutation, R240C, in the kindred. This mutation has been reported three times before, once in a family with classic MFS [Loeys et al., 2001: Arch Intern Med 161:2447-2454], once in one member of a multi-generation EL kindred, [Körkkö et al., 2002: J Med Genet 39:34-41], and once in an adult from a familial EL kindred who had EL, and involvement of the integument, without cardiovascular involvement [Comeglio et al., 2002: Br J Ophthalmol 86:1359-1362]. This is the second report of the R240C mutation in association with isolated EL, and supports the existing evidence that the R240C mutation can result in two quite distinct, yet related, phenotypes. It also raises the possibility that R240C may prove to be a relative mutational "hot-spot" for isolated EL. We review the current literature regarding EL (isolated and other) and FBN1 mutations.

Congenital diaphragmatic eventration and bilateral uretero-hydronephrosis in a patient with neonatal Marfan syndrome caused by a mutation in exon 25 of the FBN1 gene and review of the literature

Neonatal Marfan syndrome, the most severe presentation of Marfan syndrome phenotypes (MIM 154700), is characterised mainly by joint contractures, arachnodactyly, loose skin, crumpled ears, severe atrioventricular valve dysfunction and pulmonary emphysema. Death usually occurs within the first 2 years of life from congestive heart failure. We describe here a newborn male with many typical characteristics of neonatal Marfan syndrome associated with a diaphragmatic eventration and a bilateral uretero-hydronephrosis with bladder dilatation. He died from cardiac failure due to severe tricuspid and mitral regurgitation at 62 h of age.

CONCLUSION

Molecular analysis showed a heterozygous missense mutation at nucleotide 3165 (3165T>G) in exon 25 of the FBN1 gene, resulting in the substitution of cysteine for tryptophan (C1055W).

Segregation of a novel FBN1 gene mutation, G1796E, with kyphoscoliosis and radiographic evidence of vertebral dysplasia in three generations

Skeletal and spinal radiographic findings are described in five individuals of a three-generation kindred with kyphoscoliosis. The affected individuals have a novel FBN1 gene mutation, G1796E. To our knowledge, this is the first report of a family with an FBN1 gene mutation cosegregating with an unusual autosomal dominant progressive kyphoscoliosis of variable severity, together with radiological abnormalities of the spine, and some skeletal but no ocular or cardiac manifestations of Marfan syndrome. This previously undescribed phenotype represents yet another in the widening spectrum of fibrillinopathies caused by an FBN1 gene mutation.

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.

The latent transforming growth factor beta binding protein (LTBP) family

The transforming growth factor beta (TGFbeta) cytokines are a multi-functional family that exert a wide variety of effects on both normal and transformed mammalian cells. The secretion and activation of TGFbetas is regulated by their association with latency-associated proteins and latent TGFbeta binding proteins (LTBPs). Over the past few years, three members of the LTBP family have been identified, in addition to the protoype LTBP1 first sequenced in 1990. Three of the LTBP family are expressed in a variety of isoforms as a consequence of alternative splicing. This review summarizes the differences between the isoforms in terms of the effects on domain structure and hence possible function. The close identity between LTBPs and members of the fibrillin family, mutations in which have been linked directly to Marfan's syndrome, suggests that anomalous expression of LTBPs may be associated with disease. Recent data indicating that differential expression of LTBP1 isoforms occurs during the development of coronary heart disease is considered, together with evidence that modulation of LTBP function, and hence of TGFbeta activity, is associated with a variety of cancers.

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.

Cysteine substitutions in epidermal growth factor-like domains of fibrillin-1: distinct effects on biochemical and clinical phenotypes

Fibrillin-1 (FBN1) contains 47 epidermal growth factor (EGF)-like domains characterized by six conserved cysteine residues. Cysteine substitutions that disrupt one of the three disulfide bonds are frequent causes of Marfan syndrome (MFS). We identified 19 new substitutions involving cysteine residues in each of the six positions of EGF-like domains. Allele-specific mRNA assays revealed equal abundance of mutant and normal FBN1 transcripts in all 10 individuals studied. Quantitative pulse-chase analysis of fibrillin protein was performed on 25 mutant fibroblast strains with substitutions of 22 different cysteine residues in 18 different EGF-like domains spanning the entire gene. Normal synthesis and stability of mutant fibrillin molecules was seen in 20/25 individuals, 11 of whom showed delayed intracellular processing and/or secretion. In the remaining five cases, the mutant protein was apparently unstable. In four of these five cases, the second or third disulfide bond of EGF-like domains immediately preceding an 8-cysteine or hybrid domain was affected. All but two mutations caused severe reduction of matrix deposition, which was attributed to a dominant-negative effect of mutant molecules. For genotype/phenotype comparisons, clinical data on 25 probands and 19 mutation-positive family members were analyzed. Ocular manifestations were among the most consistent features (ectopia lentis in 86%, myopia in 80%). Nine mutations encoded by exons 26-32 resulted in early-onset classic MFS and, in one case, neonatal-lethal MFS. Mutations outside this region were associated with variable clinical phenotypes, including individuals with fibrillinopathies not meeting diagnostic criteria for MFS.

Novel exon skipping mutation in the fibrillin-1 gene: two 'hot spots' for the neonatal Marfan syndrome

The Marfan syndrome is an autosomal dominant heritable disorder of connective tissue that involves principally the skeletal, ocular, and cardiovascular systems. The most severe end of the phenotypic spectrum, the neonatal Marfan syndrome (nMFS), is characterized by pronounced atrioventricular valve dysfunction, and death often occurs within the first year of life due to congestive heart failure. Mutations in the gene coding for fibrillin-1, FBN1, are known to cause Marfan syndrome, and have been identified in almost all exons of FBN1. Here, we describe a novel mutation affecting the invariant + 1 position of the splice donor site in intron 31, associated with skipping of exon 31, in a patient with nMFS. Published reports of nMFS are reviewed and a strict definition for nMFS is suggested. If this definition is used, all nMFS mutations reported to date lie in one of two hot spots, comprising mainly missense mutations in FBN1 exons 24-27 and mutations causing skipping of exon 31 or 32.

Alternative splicing of exon 37 of FBN1 deletes part of an 'eight-cysteine' domain resulting in the Marfan syndrome

A child and his father had the skeletal and cardiovascular manifestations of Marfan syndrome due to a heterozygous G+5 --> T transversion in intron 37 of the FBN1 gene. Cultured dermal fibroblasts preferentially used an alternative splice site in exon 37 that resulted in the loss of the 3' 48 nucleotides of this exon. The translational reading frame was maintained with deletion of lysine 1568 to threonine 1582 and splitting of the codons for glycine 1567 and serine 1583 to yield GCC for alanine. The deletion removed two cysteine residues as well as a potential N-linked oligosaccharide attachment site from the '8-cysteine' domain encoded by exons 37 and 38.

Loss of a consensus heparin binding site by alternative splicing of latent transforming growth factor-beta binding protein-1

Latent transforming growth factor-beta binding protein-1 (LTBP-1), plays an important role in controlling localisation and activation of transforming growth factor-beta (TGF-beta). We show that alternative splicing generates a form of mRNA which lacks bases 1277-1435 (termed LTBP-1delta53). The 53 amino acids encoded by these bases include the eighth cysteine of the first cysteine repeat and a consensus heparin binding sequence. Sequencing of genomic clones showed that alternative splicing resulted from the use of an intra-exonic 3' splice acceptor site. The loss of the heparin binding site implies that LTBP-1delta53 will bind to the extracellular matrix less efficiently than LTBP-1.

Marfan Database (third edition): new mutations and new routines for the software

The Marfan database is a software that contains routines for the analysis of mutations identified in the FBN1 gene that encodes fibrillin-1. Mutations in this gene are associated not only with Marfan syndrome but also with a spectrum of overlapping disorders. The third version of the Marfan database contains 137 entries. The software has been modified to accommodate four new routines and is now accessible on the World Wide Web at http://www.umd.necker.fr

Solution structure of the transforming growth factor beta-binding protein-like module, a domain associated with matrix fibrils

Here we describe the high resolution nuclear magnetic resonance (NMR) structure of a transforming growth factor beta (TGF-beta)-binding protein-like (TB) domain, which comes from human fibrillin-1, the protein defective in the Marfan syndrome (MFS). This domain is found in fibrillins and latent TGF-beta-binding proteins (LTBPs) which are localized to fibrillar structures in the extracellular matrix. The TB domain manifests a novel fold which is globular and comprises six antiparallel beta-strands and two alpha-helices. An unusual cysteine triplet conserved in the sequences of TB domains is localized to the hydrophobic core, at the C-terminus of an alpha-helix. The structure is stabilized by four disulfide bonds which pair in a 1-3, 2-6, 4-7, 5-8 pattern, two of which are solvent exposed. Analyses of MFS-causing mutations and the fibrillin-1 cell-binding RGD site provide the first clues to the surface specificity of TB domain interactions. Modelling of a homologous TB domain from LTBP-1 (residues 1018-1080) suggests that hydrophobic contacts may play a role in its interaction with the TGF-beta1 latency-associated peptide.

Marfan Database (second edition): software and database for the analysis of mutations in the human FBN1 gene

Fibrillin is the major component of extracellular microfibrils. Mutations in the fibrillin gene on chromosome 15 (FBN1) were described at first in the heritable connective tissue disorder, Marfan syndrome (MFS). More recently, FBN1 has also been shown to harbor mutations related to a spectrum of conditions phenotypically related to MFS. These mutations are private, essentially missense, generally non-recurrent and widely distributed throughout the gene. To date no clear genotype/phenotype relationship has been observed excepted for the localization of neonatal mutations in a cluster between exons 24 and 32. The second version of the computerized Marfan database contains 89 entries. The software has been modified to accomodate new functions and routines.