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PubMed2025

Genotype-first assessment of presentation and penetrance of neurofibromatosis type 1, autosomal dominant polycystic kidney disease, and Marfan syndrome within the All of Us research program cohort.

PURPOSE: Phenotype-based ascertainment of probands in studies of Mendelian disorders may exclude individuals with mild phenotypes or that lack health care access. We explore this premise in All of Us Research Program participants with pathogenic variation causal for 3 Mendelian conditions: autosomal dominant polycystic kidney disease (ADPKD), Marfan syndrome, and neurofibromatosis type 1 (NF1). METHODS: We identified All of Us Research Program participants with putatively pathogenic variation in NF1, FBN1, PKD1, and PKD2. Concept terms were extracted from electronic health records to assess participant diagnosis and phenotype. Variant annotation and participant surveys were evaluated to identify biological and social factors differentiating diagnosed and undiagnosed individuals. RESULTS: Large proportions of individuals with pathogenic variation in NF1, FBN1, or PKD1/PKD2 lack the associated diagnosis of NF1 (47%), Marfan syndrome (58%), or ADPKD (52%), respectively. Pathogenic variants in diagnosed individuals have greater inferred deleteriousness for NF1 and ADPKD, and undiagnosed individuals had less severe phenotypes compared with diagnosed individuals for all 3 conditions. CONCLUSION: A genotype-first ascertainment of individuals in genomic research allows for a more comprehensive assessment of Mendelian disease and removes biases that confound our understanding of the penetrance and presentation of these conditions.

Humans↗
PubMed1993

Fibrillin genes map to regions of conserved mouse/human synteny on mouse chromosomes 2 and 18.

Fibrillin proteins are major structural components of the 10-nm microfibrils found in elastic and nonelastic connective tissues. Previous studies have mapped the human genes for two fibrillins to chromosome bands 15q21 (FBN1) and 5q23-q31 (FBN2) and have demonstrated that FBN1 mutations are associated with Marfan syndrome, while FBN2 is linked to the gene for congenital contractural arachnodactyly. Here, we report the isolation of genomic clones of the corresponding mouse fibrillin genes (Fbn-1 and Fbn-2). By analyzing a mapping panel of mouse x rodent somatic hybrid cell lines, we have assigned the Fbn-1 gene to mouse chromosome 2 and the Fbn-2 gene to mouse chromosome 18. We then sublocalized the fibrillin genes to bands 2F (Fbn-1) and 18D-E1 (Fbn-2) by fluorescence in situ hybridization. These regions are known to exhibit conserved synteny with the regions on human chromosomes 15 and 5 that carry the homologous human fibrillin genes. In addition, the Fbn-1 gene maps in the vicinity of the gene for a connective tissue disorder on mouse chromosome 2 called Tight-skin (Tsk).

Amino Acid Sequence↗
PubMed1994

Mutations in the fibrillin gene responsible for dominant ectopia lentis and neonatal Marfan syndrome.

Mutations in the gene coding for fibrillin on chromosome 15 (FBN1) are known to cause Marfan syndrome (MFS). A related disorder, dominant ectopia lentis (EL), has also been linked genetically to this locus. We now describe ten novel mutations of FBN1 resulting in strikingly different phenotypes. In addition to classic MFS, FBN1 mutations also give rise to EL and a severe neonatal form of MFS. Interestingly, the neonatal MFS mutations are clustered in one particular region of FBN1, possibly providing new insights into genotype-phenotype comparisons.

Adolescent↗
PubMed1994

A second locus for Marfan syndrome maps to chromosome 3p24.2-p25.

Marfan syndrome (MFS) is an autosomal dominant connective-tissue disorder characterized by skeletal, ocular and cardiovascular defects of highly variable expressivity. The diagnosis relies solely on clinical criteria requiring anomalies in at least two systems. By excluding the chromosome 15 disease locus, fibrillin 1 (FBN1), in a large French family with typical cardiovascular and skeletal anomalies, we raised the issue of genetic heterogeneity in MFS and the implication of a second locus (MFS2). Linkage analyses, performed in this family, have localized MFS2 to a region of 9 centiMorgans between D3S1293 and D3S1283, at 3p24.2-p25. In this region, the highest lod score was found with D3S2336, of 4.89 (theta = 0.05). By LINKMAP analyses, the most probable position for the second locus in MFS was at D3S2335.

Adult↗
PubMed1995

Fibrillin-2 (FBN2) mutations result in the Marfan-like disorder, congenital contractural arachnodactyly.

Congenital contractural arachnodactyly (CCA) is an autosomal dominant disorder that is phenotypically similar to Marfan syndrome (MFS) and characterized by arachnodactyly, dolichostenomelia, scoliosis, multiple congenital contractures and abnormalities of the external ears. In contrast to MFS, CCA does not affect the aorta or the eyes. Two closely related genes, FBN1 located on chromosome 15q15-21.3 and FBN2 located at 5q23-31, encode large fibrillin proteins found in extracellular matrix structures called microfibrils. The MFS is caused by mutations in FBN1, while CCA has been genetically linked to FBN2 (refs 2, 5, 6). We now describe a pair of FBN2 missense mutations in two CCA patients that cause substitution of distinct cysteine residues in separate epidermal growth-factor-like (EGF) repeats. Our study provides final proof of the association between FBN2 mutations and CCA pathology, thus establishing the role of the fibrillin-2 in extracellular matrix physiology and pathology.

Base Sequence↗
PubMed2026

Losartan shows limited benefit in preclinical models of Geleophysic dysplasia.

Geleophysic dysplasia (GD) is a rare genetic disorder characterized by short stature, joint contractures, and cardiopulmonary complications, with early mortality, and linked to mutations in ADAMTSL2 (GD1), FBN1 (GD2), or LTBP3 (GD3) genes. These mutations are hypothesized to disrupt extracellular matrix (ECM) organization and enhance transforming growth factor beta (TGF-β) signaling. Losartan, an angiotensin II receptor blocker, has been proposed to mitigate TGF-β-mediated pathologies. In this study we tested the efficacy of losartan as a therapeutic drug for GD. We evaluated losartan's therapeutic potential using Adamtsl2 p.A165T mutant mice and patient-derived fibroblasts. Survival, growth, TGF-β signaling, and ECM protein expression were assessed. Losartan did not improve survival or growth in our mutant mice. Compared with control fibroblasts, patient-derived fibroblasts showed reduced basal TGF-β1 secretion. Consistent with this finding, transcriptomic analyses did not reveal activation of the TGF-β signaling pathway, and no differences in SMAD phosphorylation were observed between patient and control cells. Losartan treatment failed to modulate TGF-β signaling or ECM protein incorporation. These results suggest limited benefits of losartan in GD and challenge the notion of TGF-β dysregulation in GD pathogenesis, indicating a need for alternative targeted therapies.

Losartan↗
PubMed1994

Analyses of truncated fibrillin caused by a 366 bp deletion in the FBN1 gene resulting in Marfan syndrome.

We studied fibrillin synthesis in cultured fibroblasts from 11 members of a three-generation family with Marfan syndrome, caused by a large in-frame deletion in FBN1 (the fibrillin gene) leading to a loss of 366 bases in the corresponding fibrillin mRNA. Metabolic labelling with [35S]Met/Cys and SDS/PAGE allowed unequivocal identification of normal and truncated fibrillin in all cell strains harbouring the deletion. In culture medium, fibrillin and its truncated counterpart were predominant, whereas their respective larger precursors were found only in traces. This proportion, however, was markedly shifted towards the normal and truncated precursors by EGTA and reversed by the addition of calcium, which confirmed the existence of profibrillin and its probably calcium-dependent conversion into fibrillin. Tunicamycin caused increased electrophoretic mobility of normal and truncated molecules without changing their apparent size differences. Intracellularly, only profibrillin was found; in the mutant cells truncated and normal profibrillin molecules were present in similar amounts and both populations were secreted and deposited simultaneously into the extracellular matrix; there, however, truncated profibrillin only became easily detectable after treatment of cells with dextran sulphate, which increased the amount of extractable profibrillin. Immunofluorescence microscopy in patients' cultures identified fibrillin-containing microfibrils which appeared to be moderately reduced both in amount and diameter. Ultrastructural analysis by rotary-shadowing and immunogold electron microscopy demonstrated the presence of numerous beaded domains reacting with fibrillin antibodies, but no intact fibrillin microfibrils in patient's cell-layer extracts, in contrast with the extensive microfibrils elaborated by control cultures. Our findings suggest, that in the patients' cell cultures all microfibrils contained the truncated fibrillin molecules.

Actin Cytoskeleton↗
PubMed1994

Abnormal fibrillin assembly by dermal fibroblasts from two patients with Marfan syndrome.

The microfibrillar glycoprotein fibrillin is linked to the Marfan syndrome, an autosomal dominant connective tissue disorder. In this study, fibrillin synthesis, deposition and assembly has been investigated in Marfan dermal fibroblast lines from two unrelated patients for whom distinct mutations in the fibrillin gene FBN1 have been identified. In patient NB, a point mutation has occurred which causes an amino acid substitution and the other patient (GK) has a deletion in one allele. The two cell lines were broadly comparable with respect to de novo fibrillin synthesis and its distribution between medium and cell layer compartments. Electrophoresis of fibrillin immunoprecipitates confirmed the presence of fibrillin in medium and cell layers. GK cells secreted an additional higher relative molecular mass fibrillin-immunoreactive component. The time-course of fibrillin secretion was similar for the two lines, but differences in fibrillin aggregation were apparent. Rotary shadowing electron microscopy of extracted cell layers demonstrated the presence of abundant and extensive microfibrils in NB cell layers. These were abnormal in their gross morphology in comparison to microfibrils isolated from control cultures. No periodic microfibrillar structures were isolated from GK cell layers. These studies underline the need to classify fibrillin defects in terms of biochemical and ultrastructural criteria. Examination of the effects of individual mutations on microfibril organization will be particularly informative in elucidating the relationship between microfibril dysfunction and the complex clinical manifestations of Marfan patients.

Cell Line↗
PubMed1995

Recurrent mis-splicing of fibrillin exon 32 in two patients with neonatal Marfan syndrome.

The Marfan syndrome (MFS) is an autosomal dominant heritable disorder of connective tissue. Variable and pleiotropic clinical features are observed in the skeletal, ocular, and cardiovascular systems. The most severe end of the phenotypic spectrum of this disorder comprises a group of patients usually diagnosed at birth, who have a life expectancy of little more than a year. To distinguish this group of patients from those with classical MFS, we refer to them as neonatal Marfan syndrome (nMFS). These infants usually die of congestive heart failure rather than aortic aneurysmal disease, the most frequent cause of morbidity and mortality in classical MFS. Defects in fibrillin, an elastin-associated microfibrillar glycoprotein, are now known to cause both the classical and neonatal forms of MFS. Here we report the recurrent mis-splicing of fibrillin (FBN1) exon 32, a precursor EGF-like calcium binding domain, in two unrelated infants with nMFS. The mis-splicing, in one patient, was due to an A-->T transversion at the -2 position of the consensus acceptor splice site; while that in the second patient was caused by a G-->A transition at the +1 position of the donor splice site. Characterization of FBN1 mutations in individuals at the most severe end of the Marfan syndrome spectrum should provide greater understanding of the multiple domains and regions of fibrillin.

Alleles↗
PubMed1994

DNA diagnostics of the Marfan syndrome: application of amplifiable polymorphic markers.

The diagnosis of Marfan syndrome (MFS) is still based on careful clinical examination. There are, however, many factors creating problems in the firm establishment of the correct diagnosis. After the identification of the defective gene in MFS, fibrillin 1 (FBN1), several mutations in this gene have been reported. Since so far all but one of the mutations in FBN1 have been family specific, a common diagnostic DNA test for all MFS patients is not to be expected in the near future. Here, we have utilized four polymorphic markers in the diagnostics in MFS families from different populations. Two of the markers, FBN1a and a novel FBN1b, are intragenic markers of FBN1 and two others, D15S103 (G113) and CYP19, are very close to and most probably flank FBN1. The combined use of the multiallelic markers proved highly useful in MFS diagnostics providing informativeness in all analysed families.

Adolescent↗
PubMed1994

An extra cysteine in one of the non-calcium-binding epidermal growth factor-like motifs of the FBN1 polypeptide is connected to a novel variant of Marfan syndrome.

We present here a family with a clinical phenotype resembling Marfan syndrome (MFS), and displaying joint contracture and episodes of knee joint effusions, but lacking the cardiovascular features of the syndrome. The phenotype of this family represents a unique mixture of connective tissue symptoms, some of which are found in classical MFS and some of which are typical of dominant ectopia lentis. Linkage analyses suggested a linkage (LOD score 2.4; theta = 0) between the phenotype of the family and a polymorphic marker in the vicinity of the fibrillin locus on chromosome 15 (FBN1). Furthermore, a novel transition mutation was identified in the FBN1 gene in all the affected members of the family. In contrast to the majority of fibrillin mutations reported so far, this mutation substitutes a cysteine for arginine, producing an extra cysteine in one of the non-calcium-binding EGF-like motifs of the fibrillin polypeptide, most probably disturbing the formation of one of the three disulfide bridges known to be essential for the normal conformation of this motif.

Adult↗
PubMed1995

A mutation in FBN1 disrupts profibrillin processing and results in isolated skeletal features of the Marfan syndrome.

Dermal fibroblasts from a 13-yr-old boy with isolated skeletal features of the Marfan syndrome were used to study fibrillin synthesis and processing. Only one half of the secreted profibrillin was proteolytically processed to fibrillin outside the cell and deposited into the extracellular matrix. Electron microscopic examination of rotary shadowed microfibrils made by the proband's fibroblasts were indistinguishable from control cells. Sequencing of the FBN1 gene revealed a heterozygous C to T transition at nucleotide 8176 resulting in the substitution of a tryptophan for an arginine (R2726W), at a site immediately adjacent to a consensus sequence recognized by a cellular protease. Six other individuals in the proband's family had the FBN1 mutation that segregated with tall stature. None of the affected individuals have cardiac or ocular manifestations of the Marfan syndrome. This mutation identifies a putative site for profibrillin to fibrillin processing, and is associated with isolated skeletal features of the Marfan syndrome, indicating that the FBN1 gene is one of the genes that determines height in the general population. The cellular effect of the mutation may be equivalent to a "null" FBN1 allele and may define the phenotype associated with FBN1 "null" alleles.

Adolescent↗
PubMed2025

Unraveling a novel FBN1 variant in Marfan syndrome with dilated aortic root manifestation.

BACKGROUND: Marfan syndrome (MFS) is a genetic disorder affecting connective tissue, with variable incidence rates. A significant portion of cases stems from novel genetic variants, while others inherit it from affected parents. OBJECTIVE: This study focuses on identifying the genetic cause of MFS in a specific family, using whole-exome sequencing (WES). METHODS: A 15-year-old male with confirmed MFS was examined, showing symptoms of palpitations and severe mitral valve regurgitation. WES was performed, followed by confirmation with Sanger sequencing. Variants were assessed for pathogenicity using bioinformatics tools and the American College of Medical Genetics and Genomics (ACMG) guidelines. RESULTS: One potentially novel pathogenic variant was found in exon 14 of the FBN1 gene: c.1676delCinsAAT, p.Ala559GlufsTer21. In silico analysis suggested a deleterious impact on protein structure and function, supporting their pathogenic classification. CONCLUSION: The identification of this novel variant highlights the importance of the FBN1 gene in MFS, especially its cardiovascular manifestations. Early intervention can improve patient outcomes, while ongoing research holds promise for further advancements in treatment for Marfan syndrome.

Humans↗
PubMed1994

Differential allelic expression of a fibrillin gene (FBN1) in patients with Marfan syndrome.

Marfan syndrome is a connective-tissue disorder affecting cardiovascular, skeletal, and ocular systems. The major Marfan locus has been identified as the FBN1 gene on chromosome 15; this codes for the extracellular-matrix protein fibrillin, a 350-kD constituent of the 8-10-nm elastin-associated microfibrils. We identified five MFS patients who were heterozygous for an RsaI restriction-site dimorphism in the 3' UTR of the FBN1 gene. This expressed variation was used to distinguish the mRNA output from each of the two FBN1 alleles in fibroblast cultures from these five patients. Three of the patients were shown to produce < 5% of the normal level of FBN1 transcripts from one of their alleles. This null-allele phenotype was not observed in 10 nonmarfanoid fibroblast cell lines.

Adult↗
PubMed1994

A compound-heterozygous Marfan patient: two defective fibrillin alleles result in a lethal phenotype.

We describe here the identification of defined mutations in both alleles of the fibrillin gene (FBN1) in a compound-heterozygote Marfan syndrome (MFS) child who had a very severe form of MFS resulting in death from cardiac failure at the age of 4 mo. The nonconsanguineous parents were both affected with MFS. The father's heterozygous point mutation has earlier been reported to result in W217G substitution, the mother was here shown to carry a heterozygous point mutation resulting in G2627R substitution, and the child had inherited both these mutations. The mutant FBN1 alleles were demonstrated to be transcribed with equal efficiency compared with the normal alleles, but metabolic labeling of fibroblast cultures from the child and both parents showed reduced biosynthesis and secretion of profibrillin. Also, the respective amounts of fibrillin in cell-culture media and extracellular-matrix extracts were markedly diminished, particularly in the cell cultures from father and child. In addition, immunofluorescence analysis of the cell cultures of all three family members revealed a drastically reduced amount of microfibrils, and virtually no visible fibrils could be seen in the case of the compound-heterozygote child. These findings demonstrate incomplete dominance of fibrillin mutations and underline the fatal consequences of the complete absence of normal fibrillin molecules in the microfibrils.

Actin Cytoskeleton↗