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Thoracic aortic aneurysms are life-threatening lesions that afflict young and old individuals alike. They frequently associate with genetic mutations and are characterized by reduced elastic fibre integrity, dysfunctional smooth muscle cells, improperly remodelled collagen and pooled mucoid material. There is a pressing need to understand better the compromised structural integrity of the aorta that results from these genetic mutations and renders the wall vulnerable to dilatation, dissection or rupture. In this paper, we compare the biaxial mechanical properties of the ascending aorta from 10 murine models: wild-type controls, acute elastase-treated, and eight models with genetic mutations affecting extracellular matrix proteins, transmembrane receptors, cytoskeletal proteins, or intracellular signalling molecules. Collectively, our data for these diverse mouse models suggest that reduced mechanical functionality, as indicated by a decreased elastic energy storage capability or reduced distensibility, does not predispose to aneurysms. Rather, despite normal or lower than normal circumferential and axial wall stresses, it appears that intramural cells in the ascending aorta of mice prone to aneurysms are unable to maintain or restore the intrinsic circumferential material stiffness, which may render the wall biomechanically vulnerable to continued dilatation and possible rupture. This finding is consistent with an underlying dysfunctional mechanosensing or mechanoregulation of the extracellular matrix, which normally endows the wall with both appropriate compliance and sufficient strength., (© 2017 The Author(s).)

Moyamoya disease (MMD) is a progressive vasculopathy characterized by occlusion of the terminal portion of the internal carotid arteries and its branches, and the formation of compensatory moyamoya collateral vessels. Homozygous mutations in GUCY1A3 have been reported as a cause of MMD and achalasia. Probands (n = 96) from unrelated families underwent sequencing of GUCY1A3. Functional studies were performed to confirm the pathogenicity of identified GUCY1A3 variants. Two affected individuals from the unrelated families were found to have compound heterozygous mutations in GUCY1A3. MM041 was diagnosed with achalasia at 4 years of age, hypertension and MMD at 18 years of age. MM149 was diagnosed with MMD and hypertension at the age of 20 months. Both individuals carry one allele that is predicted to lead to haploinsufficiency and a second allele that is predicted to produce a mutated protein. Biochemical studies of one of these alleles, GUCY1A3 Cys517Tyr, showed that the mutant protein (a subunit of soluble guanylate cyclase) has a significantly blunted signaling response with exposure to nitric oxide (NO). GUCY1A3 missense and haploinsufficiency mutations disrupt NO signaling leading to MMD and hypertension, with or without achalasia., Competing Interests: The authors declare no conflict of interest., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Marfan syndrome (MFS) due to mutations in FBN1 is a known cause of thoracic aortic aneurysms and acute aortic dissections (TAAD) associated with pleiotropic manifestations. Genetic predisposition to TAAD can also be inherited in families in the absence of syndromic features, termed familial TAAD (FTAAD), and several causative genes have been identified to date. FBN1 mutations can also be identified in FTAAD families, but the frequency of these mutations has not been established. We performed exome sequencing of 183 FTAAD families and identified pathogenic FBN1 variants in five (2.7%) of these families. We also identified eight additional FBN1 rare variants that could not be unequivocally classified as disease-causing in six families. FBN1 sequencing should be considered in individuals with FTAAD even without significant systemic features of MFS., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Almost one-quarter of patients presenting with thoracic aortic aneurysms (TAAs) or acute aortic dissections (TAADs) have an underlying mutation in a specific gene. A subset of these patients will have systemic syndromic features, for example, skeletal features in patients with Marfan Syndrome. It is important to note that the majority of patients with thoracic aortic disease will not have these syndromic features but many will have a family history of the disease. The genes predisposing to these thoracic aortic diseases are inherited in an autosomal dominant manner, and thirteen genes have been identified to date. As the clinical phenotype associated with each specific gene is defined, the data indicate that the underlying gene dictates associated syndromic features. More importantly, the underlying gene also dictates the aortic disease presentation, the risk for dissection at a given range of aortic diameters, the risk for additional vascular diseases and what specific vascular diseases occur associated with the gene. These results lead to the recommendation that the medical and surgical management of these patients be dictated by the underlying gene, and for patients with mutations in ACTA2, the specific mutation in the gene.

Mutations in ACTA2 (smooth muscle cell-specific isoform of α-actin) lead to a predisposition to thoracic aortic aneurysms and other vascular diseases. More recently, the ACTA2 R179H mutation has been described in individuals with global smooth muscle dysfunction. We report a patient heterozygous for the mutation in ACTA2 R179H who presented with megacystis at 13 weeks gestational age and, at birth, with prune-belly sequence. He also had deep skin dimples and creases on his palms and soles, a finding not previously described but possibly related to ACTA2. To our knowledge, this is the first report of the R179H mutation in ACTA2 in a child with prune-belly sequence. We think the R179H mutation in ACTA2 should be included in the differential diagnosis of individuals presenting with the sequence without an identified mechanical obstruction. Furthermore, as ACTA2 R179H has been reported in patients with severe vasculomyopathy and premature death, we recommend that molecular testing for this mutation be considered in fetuses presenting with fetal megacystis with a normal karyotype, particularly if the bladder diameter is 15 mm or more, to allow expectant parents to make an informed decision., (Copyright © 2012 Wiley Periodicals, Inc.)

Congenital contractural arachnodactyly (CCA) is an extremely rare disease, due to mutations in the FBN2 gene encoding fibrillin-2. Another member of the fibrillin family, the FBN1 gene, is involved in a broad phenotypic continuum of connective-tissue disorders including Marfan syndrome. Identifying not only what is in common but also what differentiates these two proteins should enable us to better comprehend their respective functions and better understand the multitude of diseases in which these two genes are involved. In 1995 we created a locus-specific database (LSDB) for FBN1 mutations with the Universal Mutation Database (UMD) tool. To facilitate comparison of identified mutations in these two genes and search for specific functional areas, we created an LSDB for the FBN2 gene: the UMD-FBN2 database. This database lists 26 published and six newly identified mutations that mainly comprise missense and splice-site mutations. Although the number of described FBN2 mutations was low, the frequency of joint dislocation was significantly higher with missense mutations when compared to splice site mutations., ((c) 2008 Wiley-Liss, Inc.)

Experimental and animal studies, as well as genetic mutations in man, have indicated that the development of dentition is under the control of several genes. So far, mutations in MSX1 and PAX9 have been associated with dominantly inherited forms of human tooth agenesis that mainly involve posterior teeth. We identified a large kindred with several individuals affected with molar oligodontia that was transmitted as an isolated autosomal-dominant trait. Two-point linkage analysis using DNA from the family and polymorphic marker D14S288 in chromosome 14q12 produced a maximum lod score of 2.29 at theta = 0.1. Direct sequencing of exons 2 to 4 of PAX9 revealed a cytosine insertion mutation at nucleotide 793, leading to a premature termination of translation at aa 315. Our results support the conclusion that molar oligodontia is due to allelic heterogeneity in PAX9, and these data further corroborate the role of PAX9 as an important regulator of molar development.

Congenital contractural arachnodactyly (CCA) is an autosomal dominant condition phenotypically related to Marfan syndrome (MFS). CCA is caused by mutations in FBN2, whereas MFS results from mutations in FBN1. FBN2 mRNA extracted from 12 unrelated CCA patient cell strains was screened for mutations, and FBN2 mutations were identified in six of these samples. All of the identified FBN2 mutations cluster in a limited region of the gene, a region where mutations in FBN1 produce the severe, congenital form of MFS (so-called neonatal MFS). Furthermore, three of the identified mutations occur in the FBN2 locations exactly corresponding to FBN1 mutations that have been reported in cases of neonatal MFS. These mutations indicate that this central region of both of the fibrillins plays a critical role in human embryogenesis. The limited region of FBN2 that can be mutated to cause CCA may also help to explain the rarity of CCA compared to MFS.

Congenital contractural arachnodactyly (CCA) is an autosomal dominant disorder that is phenotypically related to the Marfan syndrome. CCA has recently been shown to result from mutations in the FBN2 gene, which encodes an elastin-associated microfibrillar protein called fibrillin-2. Two siblings are reported here with classic manifestations of CCA with unaffected parents. Analysis of the FBN2 cDNA from dermal fibroblasts from one of the affected siblings revealed a heterozygous exon splicing error deleting nt 3722-3844 of the FBN2 mRNA. This cDNA deletion resulted in selective removal of one of the 43 calcium-binding EGF-like domains of the fibrillin-2 protein. Analysis of the FBN2 gene in the affected siblings' DNA indicated that the splicing error resulted from an A-to-G transition 15 nt upstream from the 3' splice site of the intron. The genomic mutation resulting in the splicing error alters a putative branch point sequence important for lariat formation, an intermediate structure of normal splicing. The mutation was detectable in DNA from the father's hair bulbs and buccal cells but not his white blood cell DNA, indicating that the father was a somatic mosaic. Analysis of transcript levels by use of dermal fibroblasts from the proband demonstrated that the FBN2 allele containing the exon deletion was expressed at a higher level than the allele inherited from the mother. These results indicate that FBN2 exon splicing errors are a cause of CCA, furthering the understanding of the molecular basis of this disorder. In addition, the demonstration of gonadal mosaicism in the FBN2 gene is important for accurate genetic counseling of families with sporadic cases of CCA. Finally, the preferential expression of the mutated FBN2 allele in dermal fibroblasts may have implications for understanding the pathogenesis and rarity of CCA.

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.

Background: Mutations in the FBN1 gene are the cause of the Marfan syndrome, an autosomal dominant disorder with skeletal, ocular, and cardiovascular complications. Aneurysms or dissections of the ascending thoracic aorta are the major cardiovascular complications of the disorder. We tested the hypothesis that FBN1 mutations cause thoracic aortic aneurysms or dissections in patients who do not have the Marfan syndrome., Methods and Results: The FBN1 gene was screened for mutations by use of genomic DNA from two patients with thoracic aortic aneurysms who did not have the Marfan syndrome. Individual FBN1 exons were amplified with intron-based exon-specific primers; the DNA fragments were screened for mutations using single-stranded conformational polymorphism analysis; and aberrantly migrating bands were sequenced directly. We identified a missense mutation in one patient, D1155N in exon 27. Dermal fibroblasts from the affected individual were used to study the effect of the missense mutation D1155N on fibrillin-1 cellular processing. The mutation decreased the amount of fibrillin-1 deposited into the pericellular matrix. A second putative FBN1 mutation was identified in the second patient, P1837S in exon 44. Although this alteration was not observed in 234 chromosomes from unrelated individuals, the alteration may represent a rare polymorphism., Conclusions: Results of these studies support the hypothesis that FBN1 mutations cause thoracic aortic aneurysms in patients who do not have the Marfan syndrome. This information is important for understanding the pathogenesis of aortic aneurysms and identification of individuals at risk for developing thoracic aortic aneurysms or dissections.