Genetic dissection of marfan syndrome and related connective tissue disorders: an update 2012

Correlation between large FBN1 deletions and severe cardiovascular phenotype in Marfan syndrome: Analysis of two novel cases and analytical review of the literature

BACKGROUND

Marfan syndrome (MFS) is a clinically heterogeneous hereditary connective tissue disorder. Severe cardiovascular manifestations (i.e., aortic aneurysm and dissection) are the most life-threatening complications. Most of the cases are caused by mutations, a minor group of which are copy number variations (CNV), in the FBN1 gene.

METHODS

Multiplex ligation-dependent probe amplification test was performed to detect CNVs in 41 MFS patients not carrying disease-causing mutations in FBN1 gene. Moreover, the association was analyzed between the localization of CNVs, the affected regulatory elements and the cardiovascular phenotypes among all cases known from the literature.

RESULTS

A large two-exon deletion (exon 46 and 47) was identified in two related patients, which was associated with a mild form of cardiovascular phenotype. Severe cardiovascular symptoms were found significantly more frequent in patients with FBN1 large deletion compared to our patients with intragenic small scale FBN1 mutation. Bioinformatic data analyses of regulatory elements located within the FBN1 gene revealed an association between the deletion of STAT3 transcription factor-binding site and cardiovascular symptoms in five out of 25 patients.

CONCLUSION

Our study demonstrated that large CNVs are often associated with severe cardiovascular manifestations in MFS and the localization of these CNVs affect the phenotype severity.

Ocular Manifestations in Patients with Sensorineural Hearing Loss

Identification of ocular manifestations in patients with sensorineural hearing loss (SNHL) can have a large impact on the outcome and treatment of pediatric patients. Due to the common co-incidence of ocular manifestations and SNHL in children, both ophthalmologic and hearing loss screening and routine examinations must be conducted to minimize adverse outcomes and worsening of pathology. Early evaluation and diagnosis is imperative for intervention and further development of the patient. Co-incidence requires a thorough evaluation that includes a comprehensive history, examination, and diagnostic testing. In this article, a literature review was conducted to analyze the presentations of various diseases and syndromes, such as Alport Syndrome, Waardenburg Syndrome, Norrie Disease, Usher Disease, Stickler Syndrome, Marfan Syndrome, Congenital Rubella, and Hereditary Optic Neuropathies. We divided the various ocular pathologies into anterior and posterior segment presentations and associated systemic findings for better understanding. Additionally, this review aims to include an update on the management of patients with both ocular and hearing loss manifestations.

Pediatric hallux valgus: An overview of history, examination, conservative, and surgical management

Pediatric hallux valgus (PHV), while relatively rare, is still often encountered by general pediatricians. Herein, we concisely summarize the existing literature regarding the pathogenesis, associated conditions, clinical diagnosis, radiographic characteristics, conservative management, and surgical management of PVH. Though PHV is generally considered benign, the progression of hallux valgus can result in complications. The presence of an open physis in the pediatric age group delineates first line treatment choices, whenever possible, as nonoperative. The general exception to this recommendation is for children with neuromuscular and connective tissues disease who may benefit from earlier surgical management. If conservative approaches fail prior to skeletal maturity, the risk of recurrence and need for revision surgery should be discussed with patients and their families before surgical referral is made. The current review was conducted to aid primary care providers in better understanding the pathogenesis, associated conditions, and intervention options available to manage PHV.

Rare Variants and Polymorphisms of FBN1 Gene May Increase the Risk of Non-Syndromic Aortic Dissection

Aortic dissection (AD) is a cardiovascular disease characterized by high mortality and poor prognosis. Although FBN1 is associated with syndromic AD, its association with non-syndromic AD remains unclear. In this study, DNA samples from 90 Chinese individuals with non-syndromic AD (60 Stanford A, 30 Stanford B types) were analyzed to determine the relationship between diverse genotypes of the FBN1 gene and non-syndromic AD. Eleven pathogenic/likely pathogenic variants (1 novel) were identified in 12.2% of patients with non-syndromic AD. Patients with positive variants suffered from AD at a younger age than those in the negative variant group. Among the six positive missense mutations associated with cysteine residue hosts, four (66.7%) were Stanford A AD, whereas two (33.3%) were Stanford B AD. Three (100%) positive splicing/truncation variant hosts were Stanford A AD. The splicing/truncation variants and missense variants involving cysteine residues in the FBN1 gene increased the risk of Stanford A AD. Ten common SNPs that increased susceptibility to AD were identified. In particular, five SNPs were detected significantly in Stanford A AD, whereas another four SNPs were significantly detected in Stanford B AD. These significant variants can function as biomarkers for the identification of patients at risk for AD. Our findings have the potential to broaden the database of positive mutations and common SNPs of FBN1 in non-syndromic AD among the Chinese population.

An adhesion G protein-coupled receptor is required in cartilaginous and dense connective tissues to maintain spine alignment

Adolescent idiopathic scoliosis (AIS) is the most common spine disorder affecting children worldwide, yet little is known about the pathogenesis of this disorder. Here, we demonstrate that genetic regulation of structural components of the axial skeleton, the intervertebral discs, and dense connective tissues (i.e., ligaments and tendons) is essential for the maintenance of spinal alignment. We show that the adhesion G protein-coupled receptor ADGRG6, previously implicated in human AIS association studies, is required in these tissues to maintain typical spine alignment in mice. Furthermore, we show that ADGRG6 regulates biomechanical properties of tendon and stimulates CREB signaling governing gene expression in cartilaginous tissues of the spine. Treatment with a cAMP agonist could mirror aspects of receptor function in culture, thus defining core pathways for regulating these axial cartilaginous and connective tissues. As ADGRG6 is a key gene involved in human AIS, these findings open up novel therapeutic opportunities for human scoliosis.

The Pathophysiological Significance of Fibulin-3

Fibulin-3 (also known as EGF-containing fibulin extracellular matrix protein 1 (EFEMP1)) is a secreted extracellular matrix glycoprotein, encoded by the EFEMP1 gene that belongs to the eight-membered fibulin protein family. It has emerged as a functionally unique member of this family, with a diverse array of pathophysiological associations predominantly centered on its role as a modulator of extracellular matrix (ECM) biology. Fibulin-3 is widely expressed in the human body, especially in elastic-fibre-rich tissues and ocular structures, and interacts with enzymatic ECM regulators, including tissue inhibitor of metalloproteinase-3 (TIMP-3). A point mutation in EFEMP1 causes an inherited early-onset form of macular degeneration called Malattia Leventinese/Doyne honeycomb retinal dystrophy (ML/DHRD). EFEMP1 genetic variants have also been associated in genome-wide association studies with numerous complex inherited phenotypes, both physiological (namely, developmental anthropometric traits) and pathological (many of which involve abnormalities of connective tissue function). Furthermore, EFEMP1 expression changes are implicated in the progression of numerous types of cancer, an area in which fibulin-3 has putative significance as a therapeutic target. Here we discuss the potential mechanistic roles of fibulin-3 in these pathologies and highlight how it may contribute to the development, structural integrity, and emergent functionality of the ECM and connective tissues across a range of anatomical locations. Its myriad of aetiological roles positions fibulin-3 as a molecule of interest across numerous research fields and may inform our future understanding and therapeutic approach to many human diseases in clinical settings.

Tall stature in children and adolescents

Tall stature is usually defined as a height beyond 97^th percentile or more than 2 SD above the mean height for age and sex in a defined population. Familiar tall stature, also known as constitutional tall stature, is the most common cause of tall stature. Overnutrition, obesity, also usually causes overgrowth. Tall stature by itself is not a pathological condition, however, there are a number of disorders associated with tall stature. Some genetic disorders and syndromes may be associated with mental retardation and various complications. Therefore, recognition of tall stature and revealing the underlying pathogenic causes and making the diagnosis are important not to miss the serious conditions and to provide adequate medical care and genetic counseling. Pathological causes for tall statute include endocrine disorders, such as excessive growth hormone secretion, hyperthyroidism, precocious puberty and lipodystrophy, chromosome disorders, such as Trisomy X (47, XXX female), Klinefelter Syndrome (47, XXY), XYY syndrome (47, XYY male) and fragile X syndrome, and syndromes and metabolic disorders, such as Marfan Syndrome, Beckwith-Wiedemann Syndrome, Simpson-Golabi-Behmel Syndrome, Sotos Syndrome and homocystinuria. Children may require growth-reductive treatment if the predicted adult height would be excessive and unacceptable. Some hormonal, high doses of sex steroids, or surgical, bilateral percutaneous epiphysiodesis of the distal femur and proximal tibia and fibula, treatment is currently available to reduce adult height.

Variants of genes encoding collagens and matrix metalloproteinase system increased the risk of aortic dissection

Aortic dissection (AD) is a devastating, heterogeneous condition of aorta. The homeostasis between collagens and matrix metalloproteases (MMPs)/tissue inhibitors of MMPs (TIMPs) system in the extracellular matrix plays an important role for structure and functions of aorta. However, our knowledge on association between variants of genes in this system and pathogenesis of AD is very limited. We analyzed all yet known coding human genes of collagens (45 genes), MMPs/TIMPs (27 genes) in 702 sporadic AD patients and in 163 matched healthy controls, by using massively targeted next-generation and Sanger sequencing. To define the pathogenesis of potential disease-causing candidate genes, we performed transcriptome sequencing and pedigree co-segregation analysis in some genes and generated Col5a2 knockout rats. We identified 257 pathogenic or likely pathogenic variants which involved 88.89% (64/72) genes in collagens-MMPs/TIMPs system and accounted for 31.05% (218/702) sporadic AD patients. In them, 84.86% patients (185/218) carried one variant, 12.84% two variants and 2.30% more than two variants. Importantly, we identified 52 novel probably pathogenic loss-of-function (LOF) variants (20 nonsense, 16 frameshift, 14 splice sites, one stop-loss, one initiation codon) in 11.06% (50/452) AD patients, which were absent in 163 controls (P=2.5×10^-5). Transcriptome sequencing revealed that identified variants induced dyshomeostasis in expression of collagens-TIMPs/MMPs systems. The Col5a2 ^-/- rats manifested growth retardation and aortic dysplasia. Our study provides a first comprehensive map of genetic alterations in collagens-MMPs/TIMPs system in sporadic AD patients and suggests that variants of these genes contribute largely to AD pathogenesis.

α-Smooth Muscle Actin and ACTA2 Gene Expressions in Vasculopathies

α-smooth muscle actin, encoded by ACTA2 gene, is an isoform of the vascular smooth muscle actins, typically expressed in the vascular smooth muscle cells contributing to vascular motility and contraction. ACTA2 gene mutations cause a diversity of diffuse vasculopathies such as thoracic aortic aneurysms and dissections as well as occlusive vascular diseases, including premature coronary artery disease and ischemic stroke. Dynamics of differentiation-specific α-smooth muscle actin in arterial smooth muscle cells and proliferation of the proteins have been well described. Although a variety of research works have been undertaken in terms of modifications of α-smooth muscle actin and mutations of ACTA2 gene and myosin, the underlying mechanisms towards the pathological processes by way of gene mutations are yet to be clarified. The purpose of the present article is to describe the phenotypes of α-smooth muscle actin and implications of ACTA2 mutations in vasculopathies in order to enhance the understanding of potential mechanisms of aortic and coronary disorders.

A FBN1 mutation association with different phenotypes of Marfan syndrome in a Chinese family

BACKGROUND

Previous studies demonstrated that patients with different FBN1 mutations often present more considerable phenotypic variation compared to different members of the related family carrying a same mutation. The purpose of our study was to identify pathogenic mutation and provide more information about genotype-phenotypic correlations in a large Chinese family with Marfan syndrome.

METHODS

15 related family members from a Chinese 4-generation pedigree with Marfan syndrome underwent physical, ophthalmologic, radiological and cardiovascular examinations. The propositus has De Bakey III aortic dissection and didn't fulfill the revised Ghent criteria for Marfan syndrome. Nine family members have ectopia lentis and their echocardiogram was normal. Five other family members have no evidence of Marfan syndrome. Genomic DNA was isolated from blood leukocytes. The exome sequencing was employed on the propositus, then the Sanger sequencing was conducted for mutation verification in other 14 participants of this family.

RESULTS

The causative mutation in FBN1 discovered in the propositus was a known heterozygous missense mutation, c.1633T>G (p.R545C), in exon 14 (NM 000138). This same mutation was also identified in all 9 ectopia lentis patients and one unaffected 8-year-old girl. However, the same mutation was not discovered in other 4 unaffected family members.

CONCLUSIONS

Our data enhance the information of genotype-phenotype correlation owing to FBN1 mutations. To our current knowledge, we firstly reported that the same FBN1 mutation, c. 1633C>T (Arg545Cys), was detected simultaneously in three different cardinal phenotypes (ectopia lentis, aortic dissection and unaffected) within one family. The unaffected girl with FBN1 mutation may presumably represent a rare case of nonpenetrance.

Marfan syndrome: current perspectives

Marfan syndrome (MFS) is a pleiotropic connective tissue disease inherited as an autosomal dominant trait, due to mutations in the FBN1 gene encoding fibrillin 1. It is an important protein of the extracellular matrix that contributes to the final structure of a microfibril. Few cases displaying an autosomal recessive transmission are reported in the world. The FBN1 gene, which is made of 66 exons, is located on chromosome 15q21.1. This review, after an introduction on the clinical manifestations that leads to the diagnosis of MFS, focuses on cardiovascular manifestations, pharmacological and surgical therapies of thoracic aortic aneurysm and/or dissection (TAAD), mechanisms underlying the progression of aneurysm or of acute dissection, and biomarkers associated with progression of TAADs. A Dutch group compared treatment with losartan, an angiotensin II receptor-1 blocker, vs no other additional treatment (COMPARE clinical trial). They observed that losartan reduces the aortic dilatation rate in patients with Marfan syndrome. Later on, they also reported that losartan exerts a beneficial effect on patients with Marfan syndrome carrying an FBN1 mutation that causes haploinsufficiency (quantitative mutation), while it has no significant effect on patients displaying dominant negative (qualitative) mutations. Moreover, a French group in a 3-year trial compared the administration of losartan vs placebo in patients with Marfan syndrome under treatment with beta-receptor blockers. They observed that losartan decreases blood pressure but has no effect on aortic diameter progression. Thus, beta-receptor blockers remain the gold standard therapy in patients with Marfan syndrome. Three potential biochemical markers are mentioned in this review: total homocysteine, serum transforming growth factor beta, and lysyl oxidase. Moreover, markers of oxidative stress measured in plasma, previously correlated with clinical features of Marfan syndrome, may be explored as potential biomarkers of clinical severity.

Shprintzen-Goldberg syndrome: a rare disorder

Shprintzen-Goldberg Syndrome is an extremely infrequent disorder of connective tissue, characterized by craniosynostosis and marfanoid features, also known as Marfanoid Craniosynostosis syndrome. The syndrome was first introduced by Sugarman and Vogel’ (1981) however, Shprintzen and Goldberg established this as a separate clinical entity in the year 1982. Since then, approximately sixty such cases have been set down in writing in the medical literature. Herein, we present a short review of literature of this rare connective disorder, in order to create awareness about this condition, as the magnitude of this disorder is not measured properly due to the paucity of literature.

A novel fibrillin 1 gene mutation leading to marfan syndrome with minimal cardiac features

Marfan syndrome is an autosomal dominant disorder of the connective tissue, characterized by early development of thoracic aortic aneurysms and/or dissections, accompanied by ocular and/or skeletal involvement, and is caused by mutations in the fibrillin 1 (FBN1) gene. We report on a patient with ectopia lentis and a nonprogressive aortic root dilatation who presented with a novel mutation affecting a conserved cysteine residue present in a calcium-binding epidermal growth factor-like domain of FBN1 (ENSP00000325527, p.Cys538Phe; Chr15:48,805,751 G>T), as revealed by complete sequencing of the FBN1 gene exons and flanking sequences. Identification of the mutation led to genetic screening of apparently asymptomatic family members, allowing the detection of characteristic ocular phenotypes in the absence of typical cardiac Marfan features. This finding stresses the importance of genetic screening of asymptomatic relatives for FBN1 gene mutation carriers.

Novel mutation in FBN1 causes ectopia lentis and varicose great saphenous vein in one Chinese autosomal dominant family

PURPOSE

To identify genetic defects in a Chinese family with ectopia lentis (EL) and varicose great saphenous vein (GSV) and to analyze the correlations between phenotype and genotype.

METHODS

Twenty-two (12 affected subjects and ten unaffected subjects) among 53 members of a Chinese family underwent complete physical, ophthalmic, and cardiovascular examinations. Genomic DNA was extracted from the leukocytes in the subjects' peripheral blood. A minimum interval was achieved with linkage study and haplotype analysis. All 65 exons and the flanking intronic regions of fibrillin-1 (FBN1) were amplified with PCR and screened for mutations with direct Sanger sequencing. Molecular modeling was analyzed in an in silico study.

RESULTS

The linkage study showed a strong cosegregation signal on chromosome 15. The non-parametric linkage analysis yielded a maximum score of 29.1(p<0.00001), and the parametric logarithm of the odds (LOD) score was 3.6. The minimum interval of the shared haplotype was rs1565863-rs877228. The best candidate gene in this region was FBN1. A novel mutation, c.3928G>A, p.1310G>S in exon 31, was identified in FBN1 and cosegregated well in the family. We applied molecular modeling to show the effect of this mutation on the fibrillin-1 structure. The mutation significantly distorts the calcium coordination, decreases the binding of the calcium ion in that motif, and affects the local calcium-binding epidermal growth factor (cbEGF) interface that depends on Ca binding.

CONCLUSIONS

FBN1-associated fibrillinopathies are a group of diseases with dynamic phenotype changes. Novel mutation p.1310G>S was first reported to cause Marfan syndrome (MFS). Our results expand the mutation spectrum in FBN1 and enhance our knowledge of genotype-phenotype correlations underlying FBN1 mutations.

Aptamers and their potential to selectively target aspects of EGF, Wnt/β-catenin and TGFβ-smad family signaling

The smooth identification and low-cost production of highly specific agents that interfere with signaling cascades by targeting an active domain in surface receptors, cytoplasmic and nuclear effector proteins, remain important challenges in biomedical research. We propose that peptide aptamers can provide a very useful and new alternative for interfering with protein–protein interactions in intracellular signal transduction cascades, including those emanating from activated receptors for growth factors. By their targeting of short, linear motif type of interactions, peptide aptamers have joined nucleic acid aptamers for use in signaling studies because of their ease of production, their stability, their high specificity and affinity for individual target proteins, and their use in high-throughput screening protocols. Furthermore, they are entering clinical trials for treatment of several complex, pathological conditions. Here, we present a brief survey of the use of aptamers in signaling pathways, in particular of polypeptide growth factors, starting with the published as well as potential applications of aptamers targeting Epidermal Growth Factor Receptor signaling. We then discuss the opportunities for using aptamers in other complex pathways, including Wnt/β-catenin, and focus on Transforming Growth Factor-β/Smad family signaling.