Cutis laxa: autosomal dominant inheritance in five generations

Material properties of the embryonic small intestine during buckling morphogenesis

During embryonic development, tissues undergo dramatic deformations as functional morphologies are stereotypically sculpted from simple rudiments. Formation of healthy, functional organs therefore requires tight control over the material properties of embryonic tissues during development, yet the biological basis of embryonic tissue mechanics is poorly understood. The present study investigates the mechanics of the embryonic small intestine, a tissue that is compactly organized in the body cavity by a mechanical instability during development, wherein differential elongation rates between the intestinal tube and its attached mesentery create compressive forces that buckle the tube into loops. The wavelength and curvature of these loops are tightly conserved for a given species. Focusing on the intestinal tube, we combined micromechanical testing with histologic analyses and enzymatic degradation experiments to conclude that elastic fibers closely associated with intestinal smooth muscle layers are responsible for the bending stiffness of the tube, and for establishing its pronounced mechanical anisotropy. These findings provide insights into the developmental role of elastic fibers in controlling tissue stiffness, and raise new questions on the physiologic function of elastic fibers in the intestine during adulthood. STATEMENT OF SIGNIFICANCE: The functional form of adult organs is established during embryogenesis through the action of physical forces on tissues with precise material properties. Despite this, however, biological control of material properties during embryogenesis is poorly understood. Focusing on the small intestine, we identified elastic fibers - rather than oriented smooth muscle - as defining bending stiffness, prescribing the lengthy intestine to be buckled precisely into compact loops for proper placement within the body cavity. We revealed a role for elastin in storing elastic energy during cell contraction, highlighting a potential role for elastin in gut motility through the ability to resist cyclic deformations associated with peristalsis. These results provide insights into intestinal development and adult function, and highlight elastin's diverse roles during organogenesis.

MATERIAL PROPERTIES OF THE EMBRYONIC SMALL INTESTINE DURING BUCKLING MORPHOGENESIS

During embryonic development, tissues undergo dramatic deformations as functional morphologies are stereotypically sculpted from simple rudiments. Formation of healthy, functional organs therefore requires tight control over the material properties of embryonic tissues during development, yet the biological basis of embryonic tissue mechanics is poorly understood. The present study investigates the mechanics of the embryonic small intestine, a tissue that is compactly organized in the body cavity by a mechanical instability during development, wherein differential elongation rates between the intestinal tube and its attached mesentery create compressive forces that buckle the tube into loops with wavelength and curvature that are tightly conserved for a given species. Focusing on the intestinal tube, we combined micromechanical testing with histologic analyses and enzymatic degradation experiments to conclude that elastic fibers closely associated with intestinal smooth muscle layers are responsible for the bending stiffness of the tube, and for establishing its pronounced mechanical anisotropy. These findings provide insights into the developmental role of elastic fibers in controlling tissue stiffness, and raise new questions on the physiologic function of elastic fibers in the intestine during adulthood.

Elastic fibers define embryonic tissue stiffness to enable buckling morphogenesis of the small intestine

During embryonic development, tissues must possess precise material properties to ensure that cell-generated forces give rise to the stereotyped morphologies of developing organs. However, the question of how material properties are established and regulated during development remains understudied. Here, we aim to address these broader questions through the study of intestinal looping, a process by which the initially straight intestinal tube buckles into loops, permitting ordered packing within the body cavity. Looping results from elongation of the tube against the constraint of an attached tissue, the dorsal mesentery, which is elastically stretched by the elongating tube to nearly triple its length. This elastic energy storage allows the mesentery to provide stable compressive forces that ultimately buckle the tube into loops. Beginning with a transcriptomic analysis of the mesentery, we identified widespread upregulation of extracellular matrix related genes during looping, including genes related to elastic fiber deposition. Combining molecular and mechanical analyses, we conclude that elastin confers tensile stiffness to the mesentery, enabling its mechanical role in organizing the developing small intestine. These results shed light on the role of elastin as a driver of morphogenesis that extends beyond its more established role in resisting cyclic deformation in adult tissues.

Cutis laxa presenting as recurrent ileus

Cutis laxa (CL) is a rare connective tissue disorder characterized by phenotypic appearance of loose and redundant skin. CL can be congenital or acquired. Congenital forms include autosomal dominant, autosomal recessive and X-linked recessive. Apart from cutaneous abnormalities, CL can present with visceral involvement. In this article, we report a case of CL presenting as recurrent ileus.

Supravalvular aortic stenosis: elastin arteriopathy

Supravalvular aortic stenosis is a systemic elastin (ELN) arteriopathy that disproportionately affects the supravalvular aorta. ELN arteriopathy may be present in a nonsyndromic condition or in syndromic conditions such as Williams-Beuren syndrome. The anatomic findings include congenital narrowing of the lumen of the aorta and other arteries, such as branches of pulmonary or coronary arteries. Given the systemic nature of the disease, accurate evaluation is recommended to establish the degree and extent of vascular involvement and to plan appropriate interventions, which are indicated whenever hemodynamically significant stenoses occur. ELN arteriopathy is genetically heterogeneous and occurs as a consequence of haploinsufficiency of the ELN gene on chromosome 7q11.23, owing to either microdeletion of the entire chromosomal region or ELN point mutations. Interestingly, there is a prevalence of premature termination mutations resulting in null alleles among ELN point mutations. The identification of the genetic defect in patients with supravalvular aortic stenosis is essential for a definitive diagnosis, prognosis, and genetic counseling.

Elastin in large artery stiffness and hypertension

Large artery stiffness, as measured by pulse wave velocity, is correlated with high blood pressure and may be a causative factor in essential hypertension. The extracellular matrix components, specifically the mix of elastin and collagen in the vessel wall, determine the passive mechanical properties of the large arteries. Elastin is organized into elastic fibers in the wall during arterial development in a complex process that requires spatial and temporal coordination of numerous proteins. The elastic fibers last the lifetime of the organism but are subject to proteolytic degradation and chemical alterations that change their mechanical properties. This review discusses how alterations in the amount, assembly, organization, or chemical properties of the elastic fibers affect arterial stiffness and blood pressure. Strategies for encouraging or reversing alterations to the elastic fibers are addressed. Methods for determining the efficacy of these strategies, by measuring elastin amounts and arterial stiffness, are summarized. Therapies that have a direct effect on arterial stiffness through alterations to the elastic fibers in the wall may be an effective treatment for essential hypertension.

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.

Looking past the lump: genetic aspects of inguinal hernia in children

Inguinal hernia is associated with a multitude of genetic syndromes. Disorders of the microfibril, elastin, collagen, and the glycosaminoglycan component of the extracellular matrix can result in an increase in the likelihood of inguinal hernia. In addition, inguinal hernia may be the presenting feature of disorders of sexual differentiation. Inguinal hernia of unknown etiology also occurs more commonly in several other groups of genetic diseases including chromosomal disorders, microdeletion disorders such as 22q11.2 microdeletion, and in single gene disorders. We review the genetics of connective tissue formation and focus on a series of genetic conditions that may present with or are characterized by a higher risk of inguinal hernia. A comprehensive review of the literature aims to provide a diagnostic framework to aid in the identification of patients with inguinal hernia as part of underlying genetic disease.

Fibrillin-1 in incisional hernias: an immunohistochemical study in scar and non-scar regions of human skin and muscle fasciae

Incisional hernias represent one of the most common complications after laparotomy. Specific pre-operative risk factors have not yet been identified. Recent studies indicate that changes in extracellular matrix components such as collagen I and collagen III may be involved in hernia development. In the present study we have evaluated the significance of fibrillin-1 in hernia development as one of the main components of the extracellular matrix. Tissue samples from non-scar skin and muscle fascia of 12 patients with incisional hernias as well as from the respective scar tissues were obtained. Corresponding tissue samples of 10 patients with normal postoperative wound healing served as controls. Distribution of fibrillin-1 was evaluated immunohistochemically. Differences in fibrillin-1 distribution in the non-scar tissues of muscle fascia have been found in patients with incisional hernia, compared to those without hernia. In scar regions of both patient groups, slight differences in the pattern of fibrillin-1 were observed. A tendency to a differential deposition of fibrillin-1 in skin samples, although hardly quantifiable, was observed as well. Our results suggest that fibrillin-1 is a relevant factor contributing to tissue stability. Disturbances in its deposition, even before scar formation, may be an important factor to the development of incisional hernias.

Association of cutis laxa and genital prolapse: a case report

Cutis laxa (CL) is an extremely inherited or acquired connective tissue disorder characterised by a markedly reduced systemic elastin content. Genital abnormalities in patients with CL have been rarely reported. We report such a case in a 48-year-old CL patient affected by genital prolapse, focusing on immunohistological and molecular biology assessment of elastin and collagen type I, III, VI content in the main uterine ligaments. The woman was referred to our department for the onset of a rapidly progressing genital prolapse and urinary incontinence. The patient underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy and sacrocolpopexy. Punch biopsies from both cardinal and uterosacral ligaments revealed a dramatic reduction in elastin and an increase in collagen type VI content. The present report seems to underline the central role exerted primarily by elastin in the supportive connective tissue and might contribute to the knowledge of extracellular matrix abnormalities at the basis of genital abnormalities in CL patients.

Sequence variant in the laminin gamma1 (LAMC1) gene associated with familial pelvic organ prolapse

Pelvic organ prolapse is a common condition, affecting up to a third of women throughout their lifetime. Genetic factors are believed to account for about 30% of the incidence, and are the least understood component of the disorder. Familial cases, particularly those in which prolapse manifests in young women, are especially valuable in the effort to find the genes involved. We recently reported autosomal dominant transmission as the most likely mode of inheritance, based on a collection of families with high incidence of prolapse. Of greatest interest was a family in which three generations of female relatives suffered from prolapse at a very young age. A genome-wide linkage scan performed using the Affymetrix GeneChip Human mapping 10K array identified ten regions with a LOD score of 1.5, the maximum possible for this family. Candidate genes within those regions were analyzed for expression in vaginal tissue by RT-PCR. Of the genes confirmed to be expressed, LAMC1 was further evaluated by sequencing and select single nucleotide polymorphism (SNP) genotyping for causative sequence variants in affected family members. We identified one such SNP, rs10911193. The rare T variant segregating with the condition is present at a frequency of 4.9% in the general population and 22% among probands from our cohort of families. It affects the binding site for NFIL3, a transcription factor that we verified to be co-expressed in vaginal tissue. Altogether these data suggest that a polymorphism in the promoter of LAMC1 may increase the susceptibility to early-onset pelvic organ prolapse.

Collagen dysregulation in the dermis of the Sagg/+ mouse: a loose skin model

The Sagg/+ mouse is an ethylnitrosourea-derived mutant with a dermal phenotype similar to some of the subtypes of Ehlers-Danlos syndrome (EDS) and cutis laxa. The dermis of the Sagg/+ mouse has less dense and more disorganized collagen fibers compared to controls. The size of extracted Type I dermal collagen was the same as that observed in normal skin; however, more collagen could be extracted from Sagg/+ skin, which also showed decreased collagen content and decreased steady-state levels of alpha1(I), alpha2(I), alpha1(V), and alpha2(V) procollagen mRNAs. The biomechanical properties of Sagg/+ skin were significantly decreased relative to normal skin. However, there were no significant differences in the quantities of the major collagen cross-links, that is, dehydrohydroxylysinonorleucine and dehydrohistidinohydroxymerodesmosine between Sagg/+ and normal skin. Electron microscopic evaluation of Sagg/+ skin indicated that the mutation interferes with the proper formation of collagen fibrils and the data are consistent with a mutation in Type V collagen leading to haploinsufficiency with the formation of two sub-populations of collagen fibrils, one normal and one with irregular shape and a larger diameter. Further study of this novel mutation will allow the identification of new mechanisms involved in the regulation of normal and pathologic collagen gene expression.

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.

Severe tortuosity and stenosis of the systemic, pulmonary and coronary vessels in 12 patients with similar phenotypic features: a new syndrome?

We describe what is, to the best of our knowledge, a previously unreported association in patients with similar facial features, skin and joint laxity, of lengthening and tortuosity of systemic, pulmonary and coronary vessels. We evaluated 12 patients with similar phenotypes, from eight different families. Detailed echocardiographic and angiographic evaluations were performed in all, and biopsies of the skin in seven. All patients have elongated facies, prominent ears, micrognathia and laxity of their joints. Angiographic pictures showed a varying degree of lengthening and tortuosity of systemic, pulmonary, and coronary arteries. Pulsatile carotid arteries formed cervical masses in 2 patients, and three had severe renal arterial stenoses. All showed varying degrees of branch and peripheral pulmonary arterial stenosis, necessitating placement of stents in six. Biopsy of the skin proved normal in all seven patients studied, thus excluding cutis laxa, Ehlers-Danlos and Marfan syndromes. The constellation of abnormalities suggests a genetic syndrome of connective tissue etiology. Further genetic studies, and gene mapping, are underway.

Cutis laxa arising from frameshift mutations in exon 30 of the elastin gene (ELN)

Congenital cutis laxa, a rare syndrome with marked skin laxity and pulmonary and cardiovascular compromise, is due to defective elastic fiber formation. In several cases, skin fibroblast tropoelastin production is markedly reduced yet reversed in vitro by transforming growth factor-beta treatment. We previously showed that this reversal was due to elastin mRNA stabilization in one cell strain, and here this behavior was confirmed in skin fibroblasts from two generations of a second family. cDNA sequencing and heteroduplex analysis of elastin gene transcripts from three fibroblast strains in two kindreds now identify two frameshift mutations (2012DeltaG and 2039DeltaC) in elastin gene exon 30, thus leading to missense C termini. No other mutations were present in the ELN cDNA sequences of all three affected individuals. Transcripts from both alleles in each kindred were unstable and responsive to transforming growth factor-beta. Exons 22, 23, 26A, and 32 were always absent. Since exon 30 underwent alternative splicing in fibroblasts, we speculate that a differential splicing pattern could conceivably lead to phenotypic rescue. These two dominant-acting, apparently de novo mutations in the elastin gene appear to be responsible for qualitative and quantitative defects in elastin, resulting in the cutis laxa phenotype.

Acquired cutis laxa associated with a plasma cell dyscrasia

Acquired cutis laxa (generalized acquired elastolysis) is characterized by skin laxity often with systemic involvement of the lungs, aorta, gastrointestinal tract, and pelvic organs. Although there have been many speculations regarding its pathogenesis, the etiology of this condition is still unclear. We describe a patient with generalized acquired cutis laxa associated with a plasma cell dyscrasia. Immunofluorescence studies were used to evaluate the pathogenesis of the elastolysis. Lesional skin was examined by direct and indirect immunofluorescence techniques for evidence of deposition of immunoglobulins on elastic fibers in the dermis. Direct immunofluorescence revealed deposition of IgG on elastic fibers in the dermis. Some patients with acquired cutis laxa have underlying lymphoreticular disorders such as plasma cell dyscrasia and may have immunoglobulins deposited on dermal elastic fibers. Immune-mediated mechanisms may play a major role in the pathogenesis of acquired cutis laxa in at least some cases.

Abnormalities of fibrillin in acquired cutis laxa

BACKGROUND

Degeneration of elastic tissue in acquired cutis laxa has been previously described, but microfibrils have not been adequately studied.

OBJECTIVE

We determined whether the microfibrillar component of elastic tissue is affected in skin of a patient with acquired cutis laxa.

METHODS

Lesional skin was examined with indirect immunofluorescence and immunoelectron microscopy with antibodies to fibrillin.

RESULTS

Indirect immunofluorescence showed a reduction in the distribution of fibrillin in the papillary dermis, where there was loss of the usual pattern of microfibrils perpendicular to the epidermis. Immunoelectron microscopy showed a typical distribution of elastic microfibrils around elastin of normal skin. In skin affected by cutis laxa microfibrils appeared morphologically normal but appeared less frequently in selected sites.

CONCLUSION

The microfibrillar component of elastic fibers was reduced in the papillary dermis of this patient with acquired cutis laxa.