Autosomal Dominant Cutis Laxa Research Articles

Novel mutation in ELN gene causes cardiac abnormalities and inguinal hernia: case report

BackgroundElastin-driven genetic diseases are a group of complex diseases driven by elastin protein insufficiency and dominant-negative production of aberrant protein, including supravalvular aortic stenosis (SVAS) and autosomal dominant cutis laxa. Here, a Chinese boy with a novel nonsense mutation in the ELN gene is reported.Case presentationWe report a 1-year-old boy who presented with exercise intolerance, weight growth restriction with age, a 1-year history of heart murmur, and inguinal hernia. Gene sequencing revealed a novel nonsense mutation in the ELN gene (c.757 C > T (p.Gln253Ter), NM_000501.4). Due to severe branch pulmonary artery stenosis, the reconstruction of the branch pulmonary artery with autologous pericardium was performed. The inguinal hernia repair was performed 3 months postoperatively. After six months of outpatient follow-up, the child recovered well, gained weight with age, and had no special clinical symptoms.ConclusionWe identified a de novo nonsense mutation in the ELN gene leading to mild SVAS and severe branch pulmonary artery stenosis. A new phenotype of inguinal hernia was also needed to be considered for possible association with the ELN gene. Still, further confirmation will be necessary.

Characterization of the Zebrafish Elastin a (elnasa12235) Mutant: A New Model of Elastinopathy Leading to Heart Valve Defects.

Elastic fibers are extracellular macromolecules that provide resilience and elastic recoil to elastic tissues and organs in vertebrates. They are composed of an elastin core surrounded by a mantle of fibrillin-rich microfibrils and are essentially produced during a relatively short period around birth in mammals. Thus, elastic fibers have to resist many physical, chemical, and enzymatic constraints occurring throughout their lives, and their high stability can be attributed to the elastin protein. Various pathologies, called elastinopathies, are linked to an elastin deficiency, such as non-syndromic supravalvular aortic stenosis (SVAS), Williams-Beuren syndrome (WBS), and autosomal dominant cutis laxa (ADCL). To understand these diseases, as well as the aging process related to elastic fiber degradation, and to test potential therapeutic molecules in order to compensate for elastin impairments, different animal models have been proposed. Considering the many advantages of using zebrafish, we here characterize a zebrafish mutant for the elastin a paralog (elnasa12235) with a specific focus on the cardiovascular system and highlight premature heart valve defects at the adult stage.

Identification of a de novo mutation of the elastin gene by targeted exome sequencing in autosomal dominant cutis laxa.

Cutis laxa (CL) comprises a heterogeneous group of entities mainly classified as X-linked, autosomal dominant and recessive forms, which differ in severity. We encountered a CL baby with no familial history. We performed targeted exome sequencing, and detected a de novo heterozygous frameshift mutation in the elastin gene of the baby.

<p>A Novel Splice-Site Mutation in the <em>ELN</em> Gene Suggests an Alternative Mechanism for Vascular Elastinopathies</p>

The ELN gene encodes elastin, a fundamental protein of the extracellular matrix that confers elasticity to different tissues including blood vessels. The formation of elastin fibers is a complex process involving monomer coacervation and subsequent crosslinking. Mutations in exons 1–29 of the ELN gene have been linked to supravalvular aortic stenosis (SVAS) whereas mutations in exons 30–33 are associated with autosomal dominant cutis laxa (ADCL). This striking segregation has led to the hypothesis that distinct molecular mechanisms underlie both diseases. SVAS is believed to arise through haploinsufficiency while ADCL is hypothesized to be caused by a dominant negative effect. Here, we describe a patient with SVAS harboring a novel splice-site mutation in the last exon of ELN. The location of this mutation is not consistent with current knowledge of SVAS, since all mutations reported in the C-terminus have been found in ADCL patients, and a thorough evaluation did not reveal significant skin involvement in this case. RT-PCR analysis of skin tissue showed that C-terminal mutations in the region can lead to the production of aberrant transcripts through intron retention and activation of cryptic splice sites and suggest that disruption of the very last exon can lead to functional haploinsufficiency potentially related to SVAS.

Supravalvular aortic stenosis as a non-syndromic familial disease. Relevance of familial screening

Supravalvular aortic stenosis (SAS) is a systemic elastin arteriopathy that may be present in a syndromic condition such as Williams–Beuren syndrome or as an isolated condition [ 1 Pieles G.E. Ofoe V. Morgan G.J. Severe left main coronary artery stenosis with abnormal branching pattern in a patient with mild supravalvar aortic stenosis and Williams–Beuren syndrome. Congenit Heart Dis. May 22 2013; https://doi.org/10.1111/chd.12087 Crossref PubMed Scopus (8) Google Scholar , 2 Merla G. Brunetti-Pierri N. Piccolo P. Micale L. Loviglio M.N. Supravalvular aortic stenosis: elastin arteriopathy. Circ Cardiovasc Genet. Dec 2012; 5: 692-696 Crossref PubMed Scopus (55) Google Scholar ]. It has also been associated with familial hypercholesterolemia [ [3] Wang Z. Yang Y. Li Z. Zhang X. Lin J. Wang L. Analysis of coronary flow haemodynamics in homozygous familial hypercholesterolaemic adolescents with aortic supravalvular stenosis. Cardiol Young. May 2012; 30: 1-6 Crossref Scopus (25) Google Scholar ]. We present the case of a 37-year-old woman with supraaortic stenosis surgically treated in which a mutation in 9 intron of elastin gene was present (Fig. 1A , transesophageal echocardiography, Fig. 1B, cardiac CT. Both techniques showing supraaortic stenosis at the level of the sinotubular junction, arrow). Familial screening revealed the same pathology in her oldest son (Fig. 1C and D, 2D transthoracic echocardiogram, supraaortic stenosis with a maximum gradient of 118 mm HG). The elastin gene encodes a protein that is one of the two components of elastic fibers. Deletions and mutations in this gene are associated with supravalvular aortic stenosis and autosomal dominant cutis laxa. The identification of the genetic defect in patients with supravalvular aortic stenosis is absolutely necessary for a definitive diagnosis, prognosis, and genetic counseling. Familial screening is mandatory.

Twenty patients including 7 probands with autosomal dominant cutis laxa confirm clinical and molecular homogeneity

BackgroundElastin gene mutations have been associated with a variety of phenotypes. Autosomal dominant cutis laxa (ADCL) is a rare disorder that presents with lax skin, typical facial characteristics, inguinal hernias, aortic root dilatation and pulmonary emphysema. In most patients, frameshift mutations are found in the 3’ region of the elastin gene (exons 30-34) which result in a C-terminally extended protein, though exceptions have been reported.MethodsWe clinically and molecularly characterized the thus far largest cohort of ADCL patients, consisting of 19 patients from six families and one sporadic patient.ResultsMolecular analysis showed C-terminal frameshift mutations in exon 30, 32, and 34 of the elastin gene and identified a mutational hotspot in exon 32 (c.2262delA). This cohort confirms the previously reported clinical constellation of skin laxity (100%), inguinal hernias (51%), aortic root dilatation (55%) and emphysema (37%).ConclusionADCL is a clinically and molecularly homogeneous disorder, but intra- and interfamilial variability in the severity of organ involvement needs to be taken into account. Regular cardiovascular and pulmonary evaluations are imperative in the clinical follow-up of these patients.

Elastic fibres in health and disease

Elastic fibres are insoluble components of the extracellular matrix of dynamic connective tissues such as skin, arteries, lungs and ligaments. They are laid down during development, and comprise a cross-linked elastin core within a template of fibrillin-based microfibrils. Their function is to endow tissues with the property of elastic recoil, and they also regulate the bioavailability of transforming growth factor β. Severe heritable elastic fibre diseases are caused by mutations in elastic fibre components; for example, mutations in elastin cause supravalvular aortic stenosis and autosomal dominant cutis laxa, mutations in fibrillin-1 cause Marfan syndrome and Weill-Marchesani syndrome, and mutations in fibulins-4 and -5 cause autosomal recessive cutis laxa. Acquired elastic fibre defects include dermal elastosis, whereas inflammatory damage to fibres contributes to pathologies such as pulmonary emphysema and vascular disease. This review outlines the latest understanding of the composition and assembly of elastic fibres, and describes elastic fibre diseases and current therapeutic approaches.

Polymorphisms in the Human Tropoelastin Gene Modify In Vitro Self-Assembly and Mechanical Properties of Elastin-Like Polypeptides

Elastin is a major structural component of elastic fibres that provide properties of stretch and recoil to tissues such as arteries, lung and skin. Remarkably, after initial deposition of elastin there is normally no subsequent turnover of this protein over the course of a lifetime. Consequently, elastic fibres must be extremely durable, able to withstand, for example in the human thoracic aorta, billions of cycles of stretch and recoil without mechanical failure. Major defects in the elastin gene (ELN) are associated with a number of disorders including Supravalvular aortic stenosis (SVAS), Williams-Beuren syndrome (WBS) and autosomal dominant cutis laxa (ADCL). Given the low turnover of elastin and the requirement for the long term durability of elastic fibres, we examined the possibility for more subtle polymorphisms in the human elastin gene to impact the assembly and long-term durability of the elastic matrix. Surveys of genetic variation resources identified 118 mutations in human ELN, 17 being non-synonymous. Introduction of two of these variants, G422S and K463R, in elastin-like polypeptides as well as full-length tropoelastin, resulted in changes in both their assembly and mechanical properties. Most notably G422S, which occurs in up to 40% of European populations, was found to enhance some elastomeric properties. These studies reveal that even apparently minor polymorphisms in human ELN can impact the assembly and mechanical properties of the elastic matrix, effects that over the course of a lifetime could result in altered susceptibility to cardiovascular disease.

Alternative Splicing and Tissue-specific Elastin Misassembly Act as Biological Modifiers of Human Elastin Gene Frameshift Mutations Associated with Dominant Cutis Laxa

Elastin is the extracellular matrix protein in vertebrates that provides elastic recoil to blood vessels, the lung, and skin. Because the elastin gene has undergone significant changes in the primate lineage, modeling elastin diseases in non-human animals can be problematic. To investigate the pathophysiology underlying a class of elastin gene mutations leading to autosomal dominant cutis laxa, we engineered a cutis laxa mutation (single base deletion) into the human elastin gene contained in a bacterial artificial chromosome. When expressed as a transgene in mice, mutant elastin was incorporated into elastic fibers in the skin and lung with adverse effects on tissue function. In contrast, only low levels of mutant protein incorporated into aortic elastin, which explains why the vasculature is relatively unaffected in this disease. RNA stability studies found that alternative exon splicing acts as a modifier of disease severity by influencing the spectrum of mutant transcripts that survive nonsense-mediated decay. Our results confirm the critical role of the C-terminal region of tropoelastin in elastic fiber assembly and suggest tissue-specific differences in the elastin assembly pathway.

New insights into the pathogenesis of autosomal‐dominant cutis laxa with report of fiveELNmutations

Autosomal dominant cutis laxa (ADCL) is characterized by a typical facial appearance and generalized loose skin folds, occasionally associated with aortic root dilatation and emphysema. We sequenced exons 28-34 of the ELN gene in five probands with ADCL features and found five de novo heterozygous mutations: c.2296_2299dupGCAG (CL-1), c.2333delC (CL-2), c.2137delG (CL-3), c.2262delA (monozygotic twin CL-4 and CL-5), and c.2124del25 (CL-6). Four probands (CL-1,-2,-3,-6) presented with progressive aortic root dilatation. CL-2 and CL-3 also had bicuspid aortic valves. CL-2 presented with severe emphysema. Electron microscopy revealed elastic fiber fragmentation and diminished dermal elastin deposition. RT-PCR studies showed stable mutant mRNA in all patients. Exon 32 skipping explains a milder phenotype in patients with exon 32 mutations. Mutant protein expression in fibroblast cultures impaired deposition of tropoelastin onto microfibril-containing fibers, and enhanced tropoelastin coacervation and globule formation leading to lower amounts of mature, insoluble elastin. Mutation-specific effects also included endoplasmic reticulum stress and increased apoptosis. Increased pSMAD2 staining in ADCL fibroblasts indicated enhanced transforming growth factor beta (TGF-β) signaling. We conclude that ADCL is a systemic disease with cardiovascular and pulmonary complications, associated with increased TGF-β signaling and mutation-specific differences in endoplasmic reticulum stress and apoptosis.

Mechanisms of emphysema in autosomal dominant cutis laxa

Heterozygous elastin gene mutations cause autosomal dominant cutis laxa associated with emphysema and aortic aneurysms. To investigate the molecular mechanisms leading to cutis laxa in vivo, we generated transgenic mice by pronuclear injection of minigenes encoding normal human tropoelastin (WT) or tropoelastin with a cutis laxa mutation (CL). Three independent founder lines of CL mice showed emphysematous pulmonary airspace enlargement. No consistent dermatological or cardiovascular pathologies were observed. One CL and one WT line were selected for detailed studies. Both mutant and control transgenic animals showed elastin deposition into pulmonary elastic fibers, indicated by increased desmosine levels in the lung and by colocalization of transgenic and endogenous elastin by immunostaining. CL mice showed increased static lung compliance and decreased stiffness of lung tissue. In addition, markers of transforming growth factor-β (TGFβ) signaling and the unfolded protein response (UPR) were elevated together with increased apoptosis in the lungs of CL animals. We conclude that the synthesis of mutant elastin in CL activates multiple downstream disease pathways by triggering a UPR, altered mechanical signaling, increased release of TGFβ and apoptosis. We propose that the combined effects of these processes lead to the development of an emphysematous pulmonary phenotype in CL.

Mutations in LTBP4 Cause a Syndrome of Impaired Pulmonary, Gastrointestinal, Genitourinary, Musculoskeletal, and Dermal Development

We report recessive mutations in the gene for the latent transforming growth factor-beta binding protein 4 (LTBP4) in four unrelated patients with a human syndrome disrupting pulmonary, gastrointestinal, urinary, musculoskeletal, craniofacial, and dermal development. All patients had severe respiratory distress, with cystic and atelectatic changes in the lungs complicated by tracheomalacia and diaphragmatic hernia. Three of the four patients died of respiratory failure. Cardiovascular lesions were mild, limited to pulmonary artery stenosis and patent foramen ovale. Gastrointestinal malformations included diverticulosis, enlargement, tortuosity, and stenosis at various levels of the intestinal tract. The urinary tract was affected by diverticulosis and hydronephrosis. Joint laxity and low muscle tone contributed to musculoskeletal problems compounded by postnatal growth delay. Craniofacial features included microretrognathia, flat midface, receding forehead, and wide fontanelles. All patients had cutis laxa. Four of the five identified LTBP4 mutations led to premature termination of translation and destabilization of the LTBP4 mRNA. Impaired synthesis and lack of deposition of LTBP4 into the extracellular matrix (ECM) caused increased transforming growth factor-beta (TGF-beta) activity in cultured fibroblasts and defective elastic fiber assembly in all tissues affected by the disease. These molecular defects were associated with blocked alveolarization and airway collapse in the lung. Our results show that coupling of TGF-beta signaling and ECM assembly is essential for proper development and is achieved in multiple human organ systems by multifunctional proteins such as LTBP4.

Analysis of Exonic Elastin Variants in Severe, Early-Onset Chronic Obstructive Pulmonary Disease

The destruction of elastic fibers has been implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Emphysema has been described in autosomal dominant cutis laxa, which can be caused by mutations in the elastin gene. Previously, a rare functional mutation in the terminal exon of elastin was found in a case of severe, early-onset COPD. To test the hypothesis that other similar elastin mutations may predispose to COPD, we screened 90 probands from the Boston Early-Onset COPD Study and 90 smoking control subjects from the Normative Aging Study for mutations in elastin exons using high-resolution DNA melt analysis followed by resequencing. Rare nonsynonymous single-nucleotide polymorphisms (SNPs) seen only in cases were examined for segregation with airflow obstruction within pedigrees. Common nonsynonymous SNPs were tested for association with COPD in a family-based analysis of 949 subjects from the Boston Early-Onset COPD Study, and in a case-control analysis in 389 COPD cases from the National Emphysema Treatment Trial and 472 control subjects from the Normative Aging Study. Of 28 elastin variants found, 3 were nonsynonymous SNPs found only in cases. The previously described Gly773Asp mutation was found in another proband. The other two SNPs did not clearly segregate with COPD within families. Two common nonsynonymous SNPs did not demonstrate significant associations in either a family-based or case-control analysis. Exonic SNPs in the elastin gene do not appear to be common risk factors for severe COPD.

Homozygous Missense Mutation in Fibulin-5 in an Iranian Autosomal Recessive Cutis Laxa Pedigree and Associated Haplotype

Cutis laxa is a rare group of inherited and acquired disorders characterized by loose and redundant skin with reduced elasticity. Mutations in the elastin coding gene have been shown to cause autosomal dominant cutis laxa in three families. A homozygous mutation in the fibulin-5 coding gene was discovered in a Turkish pedigree showing recessive inheritance, and a different mutation in this gene was found in the heterozygous state in a sporadic case of the disease. Here, we report the third case of a mutation in the fibulin-5 coding gene in a recessive Iranian cutis laxa pedigree. The mutation is the same as previously reported in the Turkish pedigree, further confirming that it is causative of disease. A haplotype consisting of seven intragenic sequence variations common to both pedigrees is described for the mutation-carrying fibulin-5 allele.

Biochemical Analysis of Elastic Fiber Formation with a Frameshift-Mutated Tropoelastin (fmTE) at the C-Terminus of Tropoelastin

Elastic fibers play an important role in characteristic elastic properties of tissues such as skin, lungs, ligaments, and blood vessels. Many of the disorders related to elastic fibers are due to errors in assembly, yet the basic mechanisms of this process remain unclear. Cutis laxa, which is caused by an elastin gene mutation, includes a rare and heterogeneous group of the disorders characterized by lax, inelastic skin. To investigate whether elastic fiber assembly insufficiency is a possible factor in cutis laxa, we compared normal tropoelastin (nTE) and frameshift-mutated tropoelastin (fmTE) from a patient with autosomal dominant cutis laxa using an in vitro elastic fiber assembly model, in which purified recombinant tropoelastin was added to the culture medium. Assembly was evaluated by immunofluorescence staining, the quantitative analysis of cross-linked amino acids, and semi-quantitative analysis of matrix-associated tropoelastin. Immunofluorescence microscopy indicated an approximate 50% decrease in the deposition of fmTE in the extracelluar matrix, in contrast to that of nTE. The amount of cross-linked amino acids unique to mature insoluble elastin in the fmTE assembly was also decreased by approximately 20%. In addition, we clarified that the molecular interaction between fmTE and the amino-terminal domain of fibrillin-1 or full-length fibulin-5 was significantly decreased. Our results suggest that the defect of fmTE fiber assembly is due, at least in part, to decreased molecular interactions between tropoelastin and the microfibrillar components fibulin-5 and fibrillin.

Autosomal Dominant Cutis Laxa with Severe Lung Disease: Synthesis and Matrix Deposition of Mutant Tropoelastin

Cutis laxa (CL) is a heterogeneous group of genetic and acquired disorders with at least two autosomal dominant forms caused by mutations in the elastin and fibulin-5 genes, respectively. To define the molecular basis of CL in patients negative for point mutations in the elastin gene, metabolic labeling and immunoprecipitation experiments were used to study the synthesis of elastin in dermal fibroblasts. In addition to the normal 68 kDa tropoelastin (TE) protein, an abnormal, 120 kDa polypeptide was detected in the proband and her affected daughter in a CL family characterized by hernias and unusually severe and early-onset pulmonary disease including bronchiectasis and pulmonary emphysema. Mutational and gene expression studies established that affected individuals in this family carried a partial tandem duplication in the elastin locus. Immunoprecipitation experiments showed that the mutant TE was partially secreted and partially retained intracellularly. A polyclonal antibody raised against a unique peptide in the mutant TE molecule showed both intracellular and matrix staining. We conclude that elastin mutations can cause CL associated with a severe pulmonary phenotype. Synthesis of abnormal TE may interfere with elastic fiber function through a dominant-negative or a gain of function mechanism.

Williams syndrome and related disorders.

Three clinical conditions displaying phenotypic overlap have been linked to mutation or deletion of the elastin gene at 7q11.23. Supravalvar aortic stenosis, an autosomal dominant disorder characterized by elastin arteriopathy, is caused by mutation or intragenic deletions of ELN resulting in loss of function. Autosomal dominant cutis laxa, a primarily cutaneous condition, is the result of frameshift mutations at ELN that cause a dominant-negative effect on elastic fiber structure. Williams syndrome, a neurodevelopmental disorder is due to a 1.5 Mb deletion that includes ELN and at least 15 contiguous genes. The disorder is characterized by dysmorphic facies, mental retardation or learning difficulties, elastin arteriopathy, a unique cognitive profile of relative strength in auditory rote memory and language and extreme weakness in visuospatial constructive cognition, and a typical personality that includes overfriendliness, anxiety, and attention problems. The understanding of these disorders has progressed from phenotypic description to identification of causative mutations and insight into pathogenetic mechanisms for some aspects of the phenotype.

An elastin gene mutation producing abnormal tropoelastin and abnormal elastic fibres in a patient with autosomal dominant cutis laxa.

Elastin is the protein responsible for the characteristic elastic properties of many tissues including the skin, lungs and large blood vessels. Loss-of-function mutations in the elastin gene are known to cause the heart defect supravalvular aortic stenosis (SVAS). We and others have identified deletions, nonsense mutations and splice site mutations in SVAS patients that abolish the function of one elastin gene. We have now identified an elastin mutation in a patient with a completely different phenotype, the rare autosomal dominant condition cutis laxa. A frameshift mutation in exon 32 of the elastin gene is predicted to replace 37 amino acids at the C-terminus of elastin by a novel sequence of 62 amino acids. mRNA and immunoprecipitation studies show that the mutant allele is expressed. Electron microscopy of skin sections shows abnormal branching and fragmentation in the amorphous elastin component, and immunocytochemistry shows reduced elastin deposition in the elastic fibres and fewer microfibrils in the dermis. These findings suggest that the mutant tropoelastin protein is synthesized, secreted and incorporated into the elastic matrix, where it alters the architecture of elastic fibres. Interference with cross-linking would reduce elastic recoil in affected tissues and explain the cutis laxa phenotype.

Congenital cutis laxa with a dominant inheritance and early onset emphysema.

Two cases (mother and daughter) are reported of autosomal dominant cutis laxa which are unusual in being associated with early onset emphysema. Both mother and daughter have been smokers and are heterozygotes for the alpha 1 antitrypsin genotype. The combination of cigarette smoking and subnormal alpha 1 antitrypsin levels may explain the pulmonary spread in these two women who have what is usually a benign form of cutis laxa limited to the skin.