Disrupted nitric oxide signaling due to GUCY1A3 mutations increases risk for moyamoya disease, achalasia and hypertension.

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.

Pathogenic FBN1 variants in familial thoracic aortic aneurysms and dissections.

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.

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.

R179H mutation in ACTA2 expanding the phenotype to include prune-belly sequence and skin manifestations.

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.

Analysis of multigenerational families with thoracic aortic aneurysms and dissections due to TGFBR1 or TGFBR2 mutations.

BACKGROUND: Mutations in the transforming growth factor beta receptor type I and II genes (TGFBR1 and TGFBR2) cause Loeys-Dietz syndrome (LDS), characterised by thoracic aortic aneurysms and dissections (TAAD), aneurysms and dissections of other arteries, craniosynostosis, cleft palate/bifid uvula, hypertelorism, congenital heart defects, arterial tortuosity, and mental retardation. TGFBR2 mutations can also cause TAAD in the absence of features of LDS in large multigenerational families, yet only sporadic LDS cases or parent-child pairs with TGFBR1 mutations have been reported to date. METHODS: The authors identified TGFBR1 missense mutations in multigenerational families with TAAD by DNA sequencing. Clinical features of affected individuals were assessed and compared with clinical features of previously described TGFBR2 families. RESULTS: Statistical analyses of the clinical features of the TGFBR1 cohort (n = 30) were compared with clinical features of TGFBR2 cohort (n = 77). Significant differences were identified in clinical presentation and survival based on gender in TGFBR1 families but not in TGFBR2 families. In families with TGFBR1 mutations, men died younger than women based on Kaplan-Meier survival curves. In addition, men presented with TAAD and women often presented with dissections and aneurysms of arteries other than the ascending thoracic aorta. The data also suggest that individuals with TGFBR2 mutations are more likely to dissect at aortic diameters <5.0 cm than individuals with TGFBR1 mutations. CONCLUSION: This study is the first to demonstrate clinical differences between patients with TGFBR1 and TGFBR2 mutations. These differences are important for the clinical management and outcome of vascular diseases in these patients.

Marfan syndrome: defective synthesis, secretion, and extracellular matrix formation of fibrillin by cultured dermal fibroblasts.

We studied the synthesis, secretion, and aggregation into the extracellular matrix of fibrillin by dermal fibroblasts from 26 probands with the Marfan syndrome. Cells from seven probands synthesized approximately half the normal amount of fibrillin when compared with intrafamilial or unrelated controls. Cells from an additional seven probands synthesized a normal amount of fibrillin but secreted the protein less efficiently than control cells. Cells from a further eight probands synthesized and secreted normal amounts of fibrillin but the protein was poorly incorporated into extracellular matrix. Cells from the remaining four probands were indistinguishable from control cells in their synthesis and processing of fibrillin. Cells from 18 family members of 10 of the probands were also studied. Cells from affected individuals in the same family had the same biochemical defect and those from unaffected family members were indistinguishable from controls. These results indicate that mutations in the gene that encodes fibrillin are responsible for the Marfan syndrome in the majority of individuals (confirming recent immunohistochemical and genetic linkage studies) and that a variety of mutations can produce the phenotype associated with the syndrome.

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.

The molecular genetics of Marfan syndrome and related disorders.

Marfan syndrome (MFS), a relatively common autosomal dominant hereditary disorder of connective tissue with prominent manifestations in the skeletal, ocular, and cardiovascular systems, is caused by mutations in the gene for fibrillin-1 (FBN1). The leading cause of premature death in untreated individuals with MFS is acute aortic dissection, which often follows a period of progressive dilatation of the ascending aorta. Recent research on the molecular physiology of fibrillin and the pathophysiology of MFS and related disorders has changed our understanding of this disorder by demonstrating changes in growth factor signalling and in matrix-cell interactions. The purpose of this review is to provide a comprehensive overview of recent advances in the molecular biology of fibrillin and fibrillin-rich microfibrils. Mutations in FBN1 and other genes found in MFS and related disorders will be discussed, and novel concepts concerning the complex and multiple mechanisms of the pathogenesis of MFS will be explained.

Comparison of 10 murine models reveals a distinct biomechanical phenotype in thoracic aortic aneurysms.

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.

Identification of a chromosome 11q23.2-q24 locus for familial aortic aneurysm disease, a genetically heterogeneous disorder.

BACKGROUND: Aortic aneurysms cause significant mortality, and >20% relate to hereditary disorders. Familial aortic aneurysm (FAA) has been described in such conditions as the Marfan and Ehlers-Danlos type IV syndromes, due to defects in the fibrillin-1 and type III procollagen genes, respectively. Other gene defects that cause isolated aneurysms, however, have not thus far been described. METHODS AND RESULTS: We studied 3 families affected by FAA. No family met the diagnostic criteria for either Marfan or Ehlers-Danlos syndrome. Echocardiography defined involvement of both the thoracic and abdominal aorta. In family ANA, candidate gene analysis excluded linkage to loci associated with aneurysm formation, including fibrillin-1, fibrillin-2, and type III procollagen, and chromosome 3p24.2-p25. Genome-wide linkage analysis identified a 2.3-cM FAA locus (FAA1) on chromosome 11q23.3-q24 with a maximum multipoint logarithm of the odds score of 4.4. In family ANB, FAA was linked to fibrillin-1. In family ANF, however, FAA was not linked to any locus previously associated with aneurysm formation, including fibrillin-1 and FAA1. CONCLUSIONS: FAA disease is genetically heterogeneous. We have identified a novel FAA locus at chromosome 11q23.3-q24, a critical step toward elucidating 1 gene defect responsible for aortic dilatation. Future characterization of the FAA1 gene will enhance our ability to achieve presymptomatic diagnosis of aortic aneurysms and will define molecular mechanisms to target therapeutics.

Familial thoracic aortic aneurysms and dissections: genetic heterogeneity with a major locus mapping to 5q13-14.

BACKGROUND: Aneurysms and dissections affecting the ascending aorta are associated primarily with degeneration of the aortic media, called medial necrosis. Families identified with dominant inheritance of thoracic aortic aneurysms and dissections (TAA/dissections) indicate that single gene mutations can cause medial necrosis in the absence of an associated syndrome. METHODS AND RESULTS: Fifteen families were identified with multiple members with TAAs/dissections. DNA from affected members from 2 of the families was used for a genome-wide search for the location of the defective gene by use of random polymorphic markers. The data were analyzed by the affected-pedigree-member method of linkage analysis. This analysis revealed 3 chromosomal loci with multiple markers demonstrating evidence of linkage to the phenotype. Linkage analysis using further markers in these regions and DNA from 15 families confirmed linkage of some of the families to 5q13-14. Genetic heterogeneity for the condition was confirmed by a heterogeneity test. Data from 9 families with the highest conditional probability of being linked to 5q were used to calculate the pairwise and multipoint logarithm of the odds (LOD) scores, with a maximum LOD of 4.74, with no recombination being obtained for the marker D5S2029. In 6 families, the phenotype was not linked to the 5q locus. CONCLUSIONS: A major locus for familial TAAs and dissections maps to 5q13-14, with the majority (9 of 15) of the families identified demonstrating evidence of linkage to this locus. The condition is genetically heterogeneous, with 6 families not demonstrating evidence of linkage to any loci previously associated with aneurysm formation.

Genetic disorders of the elastic fiber system.

Over the last decade, a considerable amount of new information has emerged describing the protein components of elastic fibers. It is now evident that elastic fibers are complex extracellular matrix polymers, composed of at least 19 different proteins that comprise both the microfibrillar and the amorphous components of elastic fibers. Mutations in three of the genes encoding the most abundant of these elastic fiber proteins result in a broad spectrum of elastic tissue phenotypes, ranging from skeletal and skin abnormalities to vascular and ocular defects. The following disorders will be discussed in this review: supravalvular aortic stenosis; Williams-Beuren syndrome; cutis laxa; Marfan syndrome; ectopia lentis; familial thoracic aortic aneurysms and dissections; MASS syndrome; isolated skeletal features of Marfan syndrome; Shprintzen-Goldberg syndrome; and congenital contractural arachnodactyly.

Reduced penetrance and variable expressivity of familial thoracic aortic aneurysms/dissections.

Autosomal dominant inheritance of thoracic aortic aneurysms and dissections occurs in subjects with Marfan syndrome, which results from mutations in the FBN1 gene on chromosome 15. A second chromosomal locus on 3p24-25 has been identified for a Marfan-like condition with thoracic aortic aneurysms. We describe here 6 families with multiple members with thoracic aortic aneurysms and dissections in the absence of the ocular and skeletal complications of Marfan syndrome. Medical records and autopsy reports on affected subjects in families with multiple members with thoracic aortic aneurysms and dissections were reviewed. Subjects in these families at risk for developing aortic disease underwent echocardiography to evaluate the aorta. The pattern of inheritance of thoracic aortic aneurysms and dissections was autosomal dominant in these families. Most affected subjects presented with aortic root dilatation or acute type I dissection, but the age of onset of disease was variable and there was decreased penetrance of the disorder. In 2 of the families, the syndrome was not linked to FBN1 or 3p24-25. Familial thoracic aortic aneurysm and dissection is an autosomal dominant condition with marked variability in the age of onset of aortic disease and decreased penetrance, making identification of affected subjects difficult. This condition is not due to mutations in the FBN1 gene or the unidentified gene on 3p24-25.

Clustering of FBN2 mutations in patients with congenital contractural arachnodactyly indicates an important role of the domains encoded by exons 24 through 34 during human 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.

FBN1 exon 2 splicing error in a patient with Marfan syndrome.

Mutations in FBN1 cause the autosomal dominant condition, Marfan syndrome. A single-base mutation that results in a skipping of exon 2 of FBN1 was found in a Marfan patient. By sequencing this proband's entire FBN1 gene and comparing the mutated DNA sequence with proband's unaffected family numbers, we confirmed this alteration was the causative mutation. The skipping of exon 2 creates a frameshift and premature termination codon, and forms a truncated fibrillin-1 composed only of 55 amino acids of N-terminus plus 45 nonsense amino acids. The mRNA transcription levels of the mutated FBN1 allele and the deposition of fibrillin-1 into extracellular matrix in fibroblast cells culture were assessed.

Distinct skeletal abnormalities in four girls with Shprintzen-Goldberg syndrome.

We describe 4 girls with Shprintzen-Goldberg syndrome. Skeletal abnormalities common to 3 of them include bowing of long bones (with a variable degree of progression over time), flare of the metaphyses, a large anterior fontanel with persistent patency into the second to fourth years of life, 13 pairs of ribs, distinct vertebral abnormalities which were absent neonatally but evolved by the second year of life, and progressive osteopenia. These abnormalities were generalized and, in one case, progressive over the first few years of life. Communicating hydrocephalus was present in all 4 cases. The eldest, an 11-year-old girl, had additional anomalies not reported previously in this syndrome, including intestinal malrotation, an anteriorly placed anus, and mild cerebral atrophy. This is the first detailed report of skeletal manifestations in this rare disorder of unknown cause. These cases, in conjunction with a review of the literature, suggest that skeletal abnormalities are common in Shprintzen-Goldberg syndrome.

Delineation of the Marfan phenotype associated with mutations in exons 23-32 of the FBN1 gene.

Marfan syndrome is a dominantly inherited connective tissue disorder with a wide range of phenotypic severity. The condition is the result of mutations in FBN1, a large gene composed of 65 exons encoding the fibrillin-1 protein. While mutations causing classic manifestations of Marfan syndrome have been identified throughout the FBN1 gene, the six previously characterized mutations resulting in the severe, perinatal lethal form of Marfan syndrome have clustered in exons 24-32 of the gene. We screened 8 patients with either neonatal Marfan syndrome or severe cardiovascular complications of Marfan syndrome for mutations in this region of the gene. Using intron-based exon-specific primers, we amplified exons 23-32 from genomic DNAs, screened these fragments by single-stranded conformational polymorphism analysis, and sequenced indicated exons. This analysis documented mutations in exons 25-27 of the FBN1 gene in 6 of these patients. These results, taken together with previously published FBN1 mutations in this region, further define the phenotype associated with mutations in exons 24-32 of the FBN1 gene, information important for the development of possible diagnostic tests and genetic counseling.

Clinicopathologic findings in congenital aneurysms of the great vessels.

We describe the clinical, histopathologic, and angiographic findings in four children with congenital abnormalities of the great vessels of unknown cause, comprising either single or multiple arterial aneurysms, aortic/arterial dilatation, vessel tortuosity, or combinations of these abnormalities. Two children had early and severe respiratory distress due to aneurysmal compression of the trachea. All children had diffuse dilatation of several arteries, and two children also had tortuosity of multiple arteries. Progression of these abnormalities was clearly evident in one child, in whom diffuse vessel irregularity and tortuosity affected intra-abdominal, and intra and extra-cranial arteries. One child died at 5 years, while the other three have undergone successful surgical repair in the first 3 months of life and are now well, between age 2.5 and 7 years. The phenotype of each child appears unique but all have in common the rare finding of aneurysms of the aorta and main pulmonary artery. Congenital aortic aneurysms did not occur as an isolated finding in any of these children.

Shprintzen-Goldberg syndrome: a clinical analysis.

Shprintzen-Goldberg syndrome is one of a group of disorders characterized by craniosynostosis and marfanoid habitus. Eleven cases were reported previously. We present 4 new patients and review one of the patients of the original report of Shprintzen and Goldberg [1982: J Craniofac Genet Dev Biol 2:65-74], 15 years later. The clinical and radiologic findings on our patients are compared with those of the previously reported patients and also with those of Furlong et al. [1987: Am J Med Genet 26:599-604] and Lacombe and Battin [1993: Clin Dysmorphol 2: 220-224], who share many of the characteristics of Shprintzen-Goldberg syndrome. Some of the clinical data are helpful in determining if the patients of Furlong et al. [1987: Am J Med Genet 26:599-604] and Lacombe and Battin [1993: Clin Dysmorphol 2: 220-224] have a separate syndrome or represent a variant of Shprintzen-Goldberg syndrome. However, radiologic investigations appear to be more specific, since an abnormality of the first and second cervical vertebrae, hydrocephalus, dilatation of the lateral ventricles, and a Chiari-I malformation of the brain were found only in the patients with Shprintzen-Goldberg syndrome. The apparently diagnostic findings of the 15 patients with this syndrome may be helpful in differentiating between Shprintzen-Goldberg syndrome and other syndromes with craniosynostosis and marfanoid habitus.